Noticed that the given example wasn't returning any information when attempting to use against a believed good install of the StackSizeController plugin. Had the server tail the console log during a repeat attempt and captured this exception message logged by Oxide:

Failed to call hook 'ItemSearchCommand' on plugin 'StackSizeController v4.1.1' (KeyNotFoundException: The given key was not present in the dictionary.)
  at System.Collections.Generic.Dictionary`2[TKey,TValue].get_Item (TKey key) [0x0001e] in <fb001e01371b4adca20013e0ac763896>:0
  at Oxide.Plugins.StackSizeController.ItemSearchCommand (Oxide.Core.Libraries.Covalence.IPlayer player, System.String command, System.String[] args) [0x000df] in <3e90747099ca42d2bbc73b4bd93b407d>:0
  at Oxide.Plugins.StackSizeController.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00074] in <3e90747099ca42d2bbc73b4bd93b407d>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <09575a60985045248bcb43b20faeeb99>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <bae5f1223fce49c493b01571c99dce02>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <bae5f1223fce49c493b01571c99dce02>:0
(Filename: ./Runtime/Export/Debug/Debug.bindings.h Line: 35)​

I have not modified my plugin .cs file or the .json config file. Pasting both file contents below to show their state at the time of error.
rustserver@games01:~/serverfiles/oxide/config$ cat StackSizeController.json
{
  "RevertStackSizesToVanillaOnUnload": true,
  "AllowStackingItemsWithDurability": true,
  "HidePrefixWithPluginNameInMessages": false,
  "GlobalStackMultiplier": 1.0,
  "CategoryStackMultipliers": {
    "Weapon": 1.0,
    "Construction": 1.0,
    "Items": 1.0,
    "Resources": 1.0,
    "Attire": 1.0,
    "Tool": 1.0,
    "Medical": 1.0,
    "Food": 1.0,
    "Ammunition": 1.0,
    "Traps": 1.0,
    "Misc": 1.0,
    "All": 1.0,
    "Common": 1.0,
    "Component": 1.0,
    "Search": 1.0,
    "Favourite": 1.0,
    "Electrical": 1.0,
    "Fun": 1.0
  },
  "IndividualItemStackMultipliers": {},
  "IndividualItemStackSize": {
    "abovegroundpool": 1,
    "aiming.module.mlrs": 1,
    "ammo.grenadelauncher.buckshot": 24,
    "ammo.grenadelauncher.he": 12,
    "ammo.grenadelauncher.smoke": 12,
    "ammo.handmade.shell": 64,
    "ammo.nailgun.nails": 64,
    "ammo.pistol": 128,
    "ammo.pistol.fire": 128,
    "ammo.pistol.hv": 128,
    "ammo.rifle": 128,
    "ammo.rifle.explosive": 128,
    "ammo.rifle.hv": 128,
    "ammo.rifle.incendiary": 128,
    "ammo.rocket.basic": 3,
    "ammo.rocket.fire": 3,
    "ammo.rocket.hv": 3,
    "ammo.rocket.mlrs": 6,
    "ammo.rocket.sam": 1000,
    "ammo.rocket.smoke": 3,
    "ammo.shotgun": 64,
    "ammo.shotgun.fire": 64,
    "ammo.shotgun.slug": 32,
    "ammo.snowballgun": 128,
    "antiradpills": 10,
    "apple": 10,
    "apple.spoiled": 1,
    "arcade.machine.chippy": 1,
    "arrow.bone": 64,
    "arrow.fire": 64,
    "arrow.hv": 64,
    "arrow.wooden": 64,
    "attire.banditguard": 1,
    "attire.bunny.onesie": 1,
    "attire.bunnyears": 1,
    "attire.hide.boots": 1,
    "attire.hide.helterneck": 1,
    "attire.hide.pants": 1,
    "attire.hide.poncho": 1,
    "attire.hide.skirt": 1,
    "attire.hide.vest": 1,
    "attire.nesthat": 1,
    "attire.ninja.suit": 1,
    "attire.reindeer.headband": 1,
    "attire.snowman.helmet": 1,
    "autoturret": 1,
    "axe.salvaged": 1,
    "bandage": 3,
    "barrelcostume": 1,
    "barricade.concrete": 10,
    "barricade.metal": 10,
    "barricade.sandbags": 10,
    "barricade.stone": 10,
    "barricade.wood": 10,
    "barricade.wood.cover": 10,
    "barricade.woodwire": 10,
    "battery.small": 1,
    "bbq": 1,
    "beachchair": 1,
    "beachparasol": 1,
    "beachtable": 1,
    "beachtowel": 1,
    "bearmeat": 20,
    "bearmeat.burned": 20,
    "bearmeat.cooked": 20,
    "bed": 1,
    "black.berry": 20,
    "black.raspberries": 1,
    "bleach": 20,
    "blood": 1000,
    "blue.berry": 20,
    "blueberries": 20,
    "blueprintbase": 1000,
    "bone.armor.suit": 1,
    "bone.club": 1,
    "bone.fragments": 1000,
    "boogieboard": 1,
    "boombox": 1,
    "boots.frog": 1,
    "botabag": 1,
    "bottle.vodka": 1,
    "bow.compound": 1,
    "bow.hunting": 1,
    "box.repair.bench": 1,
    "box.wooden": 1,
    "box.wooden.large": 1,
    "bucket.helmet": 1,
    "bucket.water": 1,
    "building.planner": 1,
    "burlap.gloves": 1,
    "burlap.gloves.new": 1,
    "burlap.headwrap": 1,
    "burlap.shirt": 1,
    "burlap.shoes": 1,
    "burlap.trousers": 1,
    "cactusflesh": 10,
    "cakefiveyear": 1,
    "campfire": 1,
    "can.beans": 10,
    "can.beans.empty": 10,
    "can.tuna": 10,
    "can.tuna.empty": 10,
    "candycane": 1,
    "candycaneclub": 1,
    "captainslog": 1,
    "car.key": 1,
    "carburetor1": 5,
    "carburetor2": 5,
    "carburetor3": 5,
    "cardtable": 1,
    "carvable.pumpkin": 1,
    "cassette": 1,
    "cassette.medium": 1,
    "cassette.short": 1,
    "cctv.camera": 64,
    "ceilinglight": 10,
    "chainsaw": 1,
    "chair": 5,
    "charcoal": 1000,
    "chicken.burned": 20,
    "chicken.cooked": 20,
    "chicken.raw": 20,
    "chicken.spoiled": 20,
    "chineselantern": 1,
    "chocholate": 10,
    "clatter.helmet": 1,
    "clone.black.berry": 50,
    "clone.blue.berry": 50,
    "clone.corn": 50,
    "clone.green.berry": 50,
    "clone.hemp": 50,
    "clone.potato": 50,
    "clone.pumpkin": 50,
    "clone.red.berry": 50,
    "clone.white.berry": 50,
    "clone.yellow.berry": 50,
    "cloth": 1000,
    "coal": 1,
    "coffeecan.helmet": 1,
    "coffin.storage": 1,
    "composter": 1,
    "computerstation": 1,
    "connected.speaker": 5,
    "corn": 20,
    "crankshaft1": 5,
    "crankshaft2": 5,
    "crankshaft3": 5,
    "cratecostume": 1,
    "crossbow": 1,
    "crude.oil": 500,
    "cupboard.tool": 1,
    "cursedcauldron": 1,
    "deer.skull.mask": 1,
    "deermeat.burned": 20,
    "deermeat.cooked": 20,
    "deermeat.raw": 20,
    "diesel_barrel": 20,
    "discoball": 5,
    "discofloor": 5,
    "discofloor.largetiles": 5,
    "diving.fins": 1,
    "diving.mask": 1,
    "diving.tank": 1,
    "diving.wetsuit": 1,
    "door.closer": 1,
    "door.double.hinged.metal": 1,
    "door.double.hinged.toptier": 1,
    "door.double.hinged.wood": 1,
    "door.hinged.industrial.a": 1,
    "door.hinged.metal": 1,
    "door.hinged.toptier": 1,
    "door.hinged.wood": 1,
    "door.key": 1,
    "dragondoorknocker": 1,
    "drone": 1,
    "dropbox": 5,
    "drumkit": 1,
    "ducttape": 20,
    "easter.bronzeegg": 10,
    "easter.goldegg": 10,
    "easter.paintedeggs": 1000,
    "easter.silveregg": 10,
    "easterbasket": 1,
    "easterdoorwreath": 1,
    "electric.andswitch": 5,
    "electric.audioalarm": 5,
    "electric.battery.rechargable.large": 1,
    "electric.battery.rechargable.medium": 1,
    "electric.battery.rechargable.small": 1,
    "electric.blocker": 5,
    "electric.button": 5,
    "electric.cabletunnel": 1,
    "electric.counter": 5,
    "electric.doorcontroller": 5,
    "electric.flasherlight": 5,
    "electric.fuelgenerator.small": 1,
    "electric.generator.small": 1,
    "electric.hbhfsensor": 1,
    "electric.heater": 5,
    "electric.igniter": 3,
    "electric.laserdetector": 5,
    "electric.orswitch": 5,
    "electric.pressurepad": 1,
    "electric.random.switch": 5,
    "electric.rf.broadcaster": 1,
    "electric.rf.receiver": 1,
    "electric.simplelight": 1,
    "electric.sirenlight": 5,
    "electric.solarpanel.large": 3,
    "electric.splitter": 5,
    "electric.sprinkler": 10,
    "electric.switch": 5,
    "electric.teslacoil": 3,
    "electric.timer": 5,
    "electric.xorswitch": 5,
    "electrical.branch": 5,
    "electrical.combiner": 5,
    "electrical.memorycell": 5,
    "elevator": 5,
    "explosive.satchel": 10,
    "explosive.timed": 10,
    "explosives": 100,
    "factorydoor": 1,
    "fat.animal": 1000,
    "fertilizer": 1000,
    "fireplace.stone": 1,
    "firework.boomer.blue": 20,
    "firework.boomer.champagne": 20,
    "firework.boomer.green": 20,
    "firework.boomer.orange": 20,
    "firework.boomer.pattern": 20,
    "firework.boomer.red": 20,
    "firework.boomer.violet": 20,
    "firework.romancandle.blue": 20,
    "firework.romancandle.green": 20,
    "firework.romancandle.red": 20,
    "firework.romancandle.violet": 20,
    "firework.volcano": 20,
    "firework.volcano.red": 20,
    "firework.volcano.violet": 20,
    "fish.anchovy": 10,
    "fish.catfish": 5,
    "fish.cooked": 20,
    "fish.herring": 10,
    "fish.minnows": 10,
    "fish.orangeroughy": 5,
    "fish.raw": 20,
    "fish.salmon": 10,
    "fish.sardine": 10,
    "fish.smallshark": 5,
    "fish.troutsmall": 10,
    "fish.yellowperch": 10,
    "fishing.tackle": 1,
    "fishingrod.handmade": 1,
    "fishtrap.small": 5,
    "flamethrower": 1,
    "flameturret": 1,
    "flare": 5,
    "flashlight.held": 1,
    "floor.grill": 10,
    "floor.ladder.hatch": 1,
    "floor.triangle.grill": 10,
    "floor.triangle.ladder.hatch": 1,
    "fluid.combiner": 5,
    "fluid.splitter": 5,
    "fluid.switch": 1,
    "fogmachine": 1,
    "frankensteins.monster.01.head": 1,
    "frankensteins.monster.01.legs": 1,
    "frankensteins.monster.01.torso": 1,
    "frankensteins.monster.02.head": 1,
    "frankensteins.monster.02.legs": 1,
    "frankensteins.monster.02.torso": 1,
    "frankensteins.monster.03.head": 1,
    "frankensteins.monster.03.legs": 1,
    "frankensteins.monster.03.torso": 1,
    "frankensteintable": 1,
    "fridge": 1,
    "fun.bass": 1,
    "fun.boomboxportable": 1,
    "fun.casetterecorder": 1,
    "fun.cowbell": 1,
    "fun.flute": 1,
    "fun.guitar": 1,
    "fun.jerrycanguitar": 1,
    "fun.tambourine": 1,
    "fun.trumpet": 1,
    "fun.tuba": 1,
    "furnace": 1,
    "furnace.large": 1,
    "fuse": 10,
    "gates.external.high.stone": 1,
    "gates.external.high.wood": 1,
    "gears": 20,
    "geiger.counter": 1,
    "generator.wind.scrap": 1,
    "ghostsheet": 1,
    "giantcandycanedecor": 1,
    "giantlollipops": 1,
    "gloweyes": 1,
    "glue": 10,
    "granolabar": 10,
    "gravestone": 1,
    "green.berry": 20,
    "grenade.beancan": 5,
    "grenade.f1": 5,
    "grenade.smoke": 3,
    "grub": 20,
    "gun.water": 1,
    "gunpowder": 1000,
    "guntrap": 1,
    "habrepair": 1,
    "halloween.candy": 1000,
    "halloween.lootbag.large": 10,
    "halloween.lootbag.medium": 10,
    "halloween.lootbag.small": 10,
    "halloween.mummysuit": 1,
    "halloween.surgeonsuit": 1,
    "hammer": 1,
    "hammer.salvaged": 1,
    "hat.beenie": 1,
    "hat.boonie": 1,
    "hat.bunnyhat": 1,
    "hat.candle": 1,
    "hat.cap": 1,
    "hat.dragonmask": 1,
    "hat.gas.mask": 1,
    "hat.miner": 1,
    "hat.oxmask": 1,
    "hat.ratmask": 1,
    "hat.wolf": 1,
    "hatchet": 1,
    "hazmatsuit": 1,
    "hazmatsuit.nomadsuit": 1,
    "hazmatsuit.spacesuit": 1,
    "hazmatsuit_scientist": 1,
    "hazmatsuit_scientist_peacekeeper": 1,
    "healingtea": 10,
    "healingtea.advanced": 10,
    "healingtea.pure": 10,
    "heavy.plate.helmet": 1,
    "heavy.plate.jacket": 1,
    "heavy.plate.pants": 1,
    "hitchtroughcombo": 1,
    "hobobarrel": 1,
    "hoodie": 1,
    "horse.armor.roadsign": 1,
    "horse.armor.wood": 1,
    "horse.saddle": 1,
    "horse.saddlebag": 1,
    "horse.shoes.advanced": 1,
    "horse.shoes.basic": 1,
    "horsedung": 100,
    "horsemeat.burned": 20,
    "horsemeat.cooked": 20,
    "horsemeat.raw": 20,
    "hosetool": 1,
    "hq.metal.ore": 1000,
    "humanmeat.burned": 20,
    "humanmeat.cooked": 20,
    "humanmeat.raw": 20,
    "humanmeat.spoiled": 20,
    "icepick.salvaged": 1,
    "industrial.wall.light": 10,
    "industrial.wall.light.green": 10,
    "industrial.wall.light.red": 10,
    "innertube": 1,
    "innertube.horse": 1,
    "innertube.unicorn": 1,
    "jacket": 1,
    "jacket.snow": 1,
    "jackhammer": 1,
    "jackolantern.angry": 1,
    "jackolantern.happy": 1,
    "jar.pickle": 10,
    "jumpsuit.suit": 1,
    "jumpsuit.suit.blue": 1,
    "kayak": 1,
    "keycard_blue": 1,
    "keycard_green": 1,
    "keycard_red": 1,
    "knife.bone": 1,
    "knife.butcher": 1,
    "knife.combat": 1,
    "ladder.wooden.wall": 5,
    "lantern": 1,
    "largecandles": 1,
    "largemedkit": 1,
    "laserlight": 5,
    "leather": 1000,
    "lmg.m249": 1,
    "lock.code": 10,
    "lock.key": 10,
    "locker": 1,
    "longsword": 1,
    "lowgradefuel": 500,
    "lumberjack hoodie": 1,
    "lunar.firecrackers": 5,
    "mace": 1,
    "machete": 1,
    "mailbox": 1,
    "map": 1,
    "mask.balaclava": 1,
    "mask.bandana": 1,
    "maxhealthtea": 10,
    "maxhealthtea.advanced": 10,
    "maxhealthtea.pure": 10,
    "meat.boar": 20,
    "meat.pork.burned": 20,
    "meat.pork.cooked": 20,
    "megaphone": 1,
    "metal.facemask": 1,
    "metal.fragments": 1000,
    "metal.ore": 1000,
    "metal.plate.torso": 1,
    "metal.refined": 100,
    "metalblade": 20,
    "metalpipe": 20,
    "metalspring": 20,
    "microphonestand": 5,
    "minihelicopter.repair": 1,
    "mining.pumpjack": 1,
    "mining.quarry": 1,
    "mixingtable": 1,
    "mlrs": 1,
    "mobilephone": 1,
    "modularcarlift": 1,
    "movembermoustache": 1,
    "movembermoustachecard": 1,
    "multiplegrenadelauncher": 1,
    "mushroom": 10,
    "newyeargong": 1,
    "nightvisiongoggles": 1,
    "note": 1,
    "oretea": 10,
    "oretea.advanced": 10,
    "oretea.pure": 10,
    "paddle": 1,
    "paddlingpool": 1,
    "pants": 1,
    "pants.shorts": 1,
    "paper": 1000,
    "partyhat": 1,
    "photo": 1,
    "photoframe.landscape": 1,
    "photoframe.large": 1,
    "photoframe.portrait": 1,
    "piano": 1,
    "pickaxe": 1,
    "pistol.eoka": 1,
    "pistol.m92": 1,
    "pistol.nailgun": 1,
    "pistol.python": 1,
    "pistol.revolver": 1,
    "pistol.semiauto": 1,
    "pistol.water": 1,
    "piston1": 10,
    "piston2": 10,
    "piston3": 10,
    "pitchfork": 1,
    "planter.large": 10,
    "planter.small": 10,
    "plantfiber": 1000,
    "pookie.bear": 1,
    "potato": 20,
    "powered.water.purifier": 1,
    "propanetank": 5,
    "pumpkin": 20,
    "pumpkinbasket": 1,
    "radiationremovetea": 10,
    "radiationremovetea.advanced": 10,
    "radiationremovetea.pure": 10,
    "radiationresisttea": 10,
    "radiationresisttea.advanced": 10,
    "radiationresisttea.pure": 10,
    "red.berry": 20,
    "research.table": 1,
    "researchpaper": 1000,
    "rf.detonator": 1,
    "rf_pager": 1,
    "rifle.ak": 1,
    "rifle.bolt": 1,
    "rifle.l96": 1,
    "rifle.lr300": 1,
    "rifle.m39": 1,
    "rifle.semiauto": 1,
    "riflebody": 10,
    "riot.helmet": 1,
    "roadsign.gloves": 1,
    "roadsign.jacket": 1,
    "roadsign.kilt": 1,
    "roadsigns": 20,
    "rock": 1,
    "rocket.launcher": 1,
    "rope": 50,
    "rug": 1,
    "rug.bear": 1,
    "rustige_egg_a": 1,
    "rustige_egg_b": 1,
    "rustige_egg_c": 1,
    "rustige_egg_d": 1,
    "rustige_egg_e": 1,
    "salvaged.cleaver": 1,
    "salvaged.sword": 1,
    "samsite": 1,
    "santabeard": 1,
    "santahat": 1,
    "scarecrow": 5,
    "scarecrow.suit": 1,
    "scarecrowhead": 1,
    "scientistsuit_heavy": 1,
    "scrap": 1000,
    "scraptea": 10,
    "scraptea.advanced": 10,
    "scraptea.pure": 10,
    "scraptransportheli.repair": 1,
    "searchlight": 1,
    "secretlabchair": 5,
    "seed.black.berry": 50,
    "seed.blue.berry": 50,
    "seed.corn": 50,
    "seed.green.berry": 50,
    "seed.hemp": 50,
    "seed.potato": 50,
    "seed.pumpkin": 50,
    "seed.red.berry": 50,
    "seed.white.berry": 50,
    "seed.yellow.berry": 50,
    "semibody": 10,
    "sewingkit": 20,
    "sheetmetal": 20,
    "shelves": 10,
    "shirt.collared": 1,
    "shirt.tanktop": 1,
    "shoes.boots": 1,
    "shotgun.double": 1,
    "shotgun.pump": 1,
    "shotgun.spas12": 1,
    "shotgun.waterpipe": 1,
    "shutter.metal.embrasure.a": 20,
    "shutter.metal.embrasure.b": 20,
    "shutter.wood.a": 20,
    "sickle": 1,
    "sign.hanging": 5,
    "sign.hanging.banner.large": 5,
    "sign.hanging.ornate": 5,
    "sign.neon.125x125": 5,
    "sign.neon.125x215": 5,
    "sign.neon.125x215.animated": 1,
    "sign.neon.xl": 1,
    "sign.neon.xl.animated": 5,
    "sign.pictureframe.landscape": 5,
    "sign.pictureframe.portrait": 5,
    "sign.pictureframe.tall": 5,
    "sign.pictureframe.xl": 5,
    "sign.pictureframe.xxl": 5,
    "sign.pole.banner.large": 5,
    "sign.post.double": 5,
    "sign.post.single": 5,
    "sign.post.town": 5,
    "sign.post.town.roof": 5,
    "sign.wooden.huge": 5,
    "sign.wooden.large": 5,
    "sign.wooden.medium": 5,
    "sign.wooden.small": 5,
    "skull": 1,
    "skull.human": 1,
    "skull.trophy": 1,
    "skull.trophy.jar": 1,
    "skull.trophy.jar2": 1,
    "skull.trophy.table": 1,
    "skull.wolf": 1,
    "skull_fire_pit": 1,
    "skulldoorknocker": 1,
    "skullspikes": 1,
    "skullspikes.candles": 1,
    "skullspikes.pumpkin": 1,
    "sled": 1,
    "sled.xmas": 1,
    "sleepingbag": 1,
    "small.oil.refinery": 1,
    "smallcandles": 1,
    "smallwaterbottle": 1,
    "smart.alarm": 5,
    "smart.switch": 5,
    "smg.2": 1,
    "smg.mp5": 1,
    "smg.thompson": 1,
    "smgbody": 10,
    "snowball": 1,
    "snowballgun": 1,
    "snowmachine": 1,
    "snowman": 5,
    "sofa": 2,
    "sofa.pattern": 2,
    "soundlight": 5,
    "sparkplug1": 20,
    "sparkplug2": 20,
    "sparkplug3": 20,
    "spear.stone": 1,
    "spear.wooden": 1,
    "speargun": 1,
    "speargun.spear": 64,
    "spiderweb": 10,
    "spikes.floor": 10,
    "spinner.wheel": 1,
    "spookyspeaker": 1,
    "stash.small": 5,
    "sticks": 100,
    "stocking.large": 1,
    "stocking.small": 5,
    "stone.pickaxe": 1,
    "stonehatchet": 1,
    "stones": 1000,
    "storage.monitor": 1,
    "strobelight": 1,
    "submarine.torpedo.straight": 100,
    "submarineduo": 1,
    "submarinesolo": 1,
    "sulfur": 1000,
    "sulfur.ore": 1000,
    "sunglasses": 1,
    "sunglasses02black": 1,
    "sunglasses02camo": 1,
    "sunglasses02red": 1,
    "sunglasses03black": 1,
    "sunglasses03chrome": 1,
    "sunglasses03gold": 1,
    "supply.signal": 1,
    "surveycharge": 10,
    "syringe.medical": 2,
    "table": 1,
    "tactical.gloves": 1,
    "target.reactive": 1,
    "targeting.computer": 64,
    "tarp": 20,
    "techparts": 50,
    "telephone": 1,
    "tool.binoculars": 1,
    "tool.camera": 1,
    "tool.instant_camera": 1,
    "toolgun": 1,
    "torch": 1,
    "trap.bear": 3,
    "trap.landmine": 5,
    "tshirt": 1,
    "tshirt.long": 1,
    "tunalight": 1,
    "twitch.headset": 1,
    "twitchsunglasses": 1,
    "valve1": 15,
    "valve2": 15,
    "valve3": 15,
    "vehicle.1mod.cockpit": 1,
    "vehicle.1mod.cockpit.armored": 1,
    "vehicle.1mod.cockpit.with.engine": 1,
    "vehicle.1mod.engine": 1,
    "vehicle.1mod.flatbed": 1,
    "vehicle.1mod.passengers.armored": 1,
    "vehicle.1mod.rear.seats": 1,
    "vehicle.1mod.storage": 1,
    "vehicle.1mod.taxi": 1,
    "vehicle.2mod.camper": 1,
    "vehicle.2mod.flatbed": 1,
    "vehicle.2mod.fuel.tank": 1,
    "vehicle.2mod.passengers": 1,
    "vehicle.chassis": 1,
    "vehicle.chassis.2mod": 1,
    "vehicle.chassis.3mod": 1,
    "vehicle.chassis.4mod": 1,
    "vehicle.module": 1,
    "vending.machine": 1,
    "wall.external.high": 10,
    "wall.external.high.ice": 10,
    "wall.external.high.stone": 10,
    "wall.frame.cell": 10,
    "wall.frame.cell.gate": 1,
    "wall.frame.fence": 10,
    "wall.frame.fence.gate": 1,
    "wall.frame.garagedoor": 1,
    "wall.frame.netting": 5,
    "wall.frame.shopfront": 1,
    "wall.frame.shopfront.metal": 1,
    "wall.graveyard.fence": 10,
    "wall.ice.wall": 10,
    "wall.window.bars.metal": 10,
    "wall.window.bars.toptier": 10,
    "wall.window.bars.wood": 10,
    "wall.window.glass.reinforced": 10,
    "watchtower.wood": 5,
    "water": 2147483647,
    "water.barrel": 1,
    "water.catcher.large": 1,
    "water.catcher.small": 1,
    "water.purifier": 1,
    "water.salt": 2147483647,
    "waterjug": 1,
    "waterpump": 1,
    "weapon.mod.8x.scope": 1,
    "weapon.mod.flashlight": 1,
    "weapon.mod.holosight": 1,
    "weapon.mod.lasersight": 1,
    "weapon.mod.muzzleboost": 1,
    "weapon.mod.muzzlebrake": 1,
    "weapon.mod.silencer": 1,
    "weapon.mod.simplesight": 1,
    "weapon.mod.small.scope": 1,
    "white.berry": 20,
    "wiretool": 1,
    "wolfmeat.burned": 20,
    "wolfmeat.cooked": 20,
    "wolfmeat.raw": 20,
    "wolfmeat.spoiled": 20,
    "wood": 1000,
    "wood.armor.helmet": 1,
    "wood.armor.jacket": 1,
    "wood.armor.pants": 1,
    "woodcross": 1,
    "woodtea": 10,
    "woodtea.advanced": 10,
    "woodtea.pure": 10,
    "workbench1": 1,
    "workbench2": 1,
    "workbench3": 1,
    "workcart": 1,
    "worm": 20,
    "wrappedgift": 1,
    "wrappingpaper": 1,
    "xmas.advent": 1,
    "xmas.decoration.baubels": 1,
    "xmas.decoration.candycanes": 1,
    "xmas.decoration.gingerbreadmen": 1,
    "xmas.decoration.lights": 1,
    "xmas.decoration.pinecone": 1,
    "xmas.decoration.star": 1,
    "xmas.decoration.tinsel": 1,
    "xmas.door.garland": 10,
    "xmas.double.door.garland": 10,
    "xmas.lightstring": 20,
    "xmas.lightstring.advanced": 150,
    "xmas.present.large": 1,
    "xmas.present.medium": 5,
    "xmas.present.small": 10,
    "xmas.tree": 1,
    "xmas.window.garland": 10,
    "xmasdoorwreath": 1,
    "xylophone": 1,
    "yellow.berry": 20
  },
  "VersionNumber": {
    "Major": 4,
    "Minor": 1,
    "Patch": 1
  }​

 


rustserver@games01:~/serverfiles/oxide/plugins$ cat StackSizeController.cs
using System;
using System.Collections.Generic;
using System.Linq;
using Newtonsoft.Json;
using Oxide.Core;
using Oxide.Core.Libraries;
using Oxide.Core.Libraries.Covalence;
using Oxide.Core.Plugins;
using UnityEngine;

namespace Oxide.Plugins
{
    [Info("Stack Size Controller", "AnExiledDev", "4.1.1")]
    [Description("Allows configuration of most items max stack size.")]
    class StackSizeController : CovalencePlugin
    {
        [PluginReference]
        Plugin AirFuel, GetToDaChoppa, VehicleVendorOptions;

        private const string _vanillaDefaultsUri = "https://raw.githubusercontent.com/AnExiledDev/StackSizeController/master/vanilla-defaults.json";

        private Configuration _config;
        private Dictionary<string, int> _vanillaDefaults;

        private readonly List<string> _ignoreList = new List<string>
        {
            "water",
            "water.salt",
            "cardtable",
            "hat.bunnyhat",
            "rustige_egg_e"
        };

        private void Init()
        {
            _config = Config.ReadObject<Configuration>();

            if (_config == null)
            {
                Log("Generating Default Config File.");

                LoadDefaultConfig();
            }

            DownloadVanillaDefaults();
            EnsureConfigIntegrity();

            AddCovalenceCommand("stacksizecontroller.setstack", nameof(SetStackCommand),
                "stacksizecontroller.setstack");
            AddCovalenceCommand("stacksizecontroller.setstackcat", nameof(SetStackCategoryCommand),
                "stacksizecontroller.setstackcat");
            AddCovalenceCommand("stacksizecontroller.setallstacks", nameof(SetAllStacksCommand),
                "stacksizecontroller.setallstacks");
            AddCovalenceCommand("stacksizecontroller.itemsearch", nameof(ItemSearchCommand),
                "stacksizecontroller.itemsearch");
            AddCovalenceCommand("stacksizecontroller.listcategories", nameof(ListCategoriesCommand),
                "stacksizecontroller.listcategories");
            AddCovalenceCommand("stacksizecontroller.listcategoryitems", nameof(ListCategoryItemsCommand),
                "stacksizecontroller.listcategoryitems");
            AddCovalenceCommand("stacksizecontroller.vd", nameof(GenerateVanillaStackSizeFileCommand),
                "stacksizecontroller.vd");
        }

        private void Unload()
        {
            if (_config.RevertStackSizesToVanillaOnUnload)
            {
                RevertStackSizes();
            }
        }

        #region Configuration

        private class Configuration
        {
            public bool RevertStackSizesToVanillaOnUnload = true;
            public bool AllowStackingItemsWithDurability = true;
            public bool HidePrefixWithPluginNameInMessages;

            public float GlobalStackMultiplier = 1;
            public Dictionary<string, float> CategoryStackMultipliers = GetCategoriesAndDefaults(1)
                .ToDictionary(k => k.Key,
                    k => Convert.ToSingle(k.Value));
            public Dictionary<string, float> IndividualItemStackMultipliers = new Dictionary<string, float>();

            public Dictionary<string, int> IndividualItemStackSize = new Dictionary<string, int>();

            public VersionNumber VersionNumber;
        }

        private static Dictionary<string, object> GetCategoriesAndDefaults(object defaultValue)
        {
            Dictionary<string, object> categoryDefaults = new Dictionary<string, object>();

            foreach (string category in Enum.GetNames(typeof(ItemCategory)))
            {
                categoryDefaults.Add(category, defaultValue);
            }

            return categoryDefaults;
        }

        protected override void SaveConfig()
        {
            Config.WriteObject(_config);
        }

        protected override void LoadDefaultConfig()
        {
            Configuration defaultConfig = GetDefaultConfig();
            defaultConfig.VersionNumber = Version;

            Config.WriteObject(defaultConfig);

            _config = Config.ReadObject<Configuration>();
        }

        private void EnsureConfigIntegrity()
        {
            Configuration configDefault = new Configuration();

            if (_config.CategoryStackMultipliers == null)
            {
                _config.CategoryStackMultipliers = configDefault.CategoryStackMultipliers;
            }

            if (_config.IndividualItemStackMultipliers == null)
            {
                _config.IndividualItemStackMultipliers = configDefault.IndividualItemStackMultipliers;
            }

            _config.VersionNumber = Version;
            SaveConfig();
        }

        private Configuration GetDefaultConfig()
        {
            return new Configuration();
        }

        private void UpdateIndividualItemStackMultiplier(int itemId, float multiplier)
        {
            if (_config.IndividualItemStackMultipliers.ContainsKey(itemId.ToString()))
            {
                _config.IndividualItemStackMultipliers[itemId.ToString()] = multiplier;

                SaveConfig();

                return;
            }

            _config.IndividualItemStackMultipliers.Add(ItemManager.itemDictionary[itemId].shortname, multiplier);

            SaveConfig();
        }

        private void UpdateIndividualItemStackMultiplier(string shortname, float multiplier)
        {
            if (_config.IndividualItemStackMultipliers.ContainsKey(shortname))
            {
                _config.IndividualItemStackMultipliers[shortname] = multiplier;

                SaveConfig();

                return;
            }

            _config.IndividualItemStackMultipliers.Add(shortname, multiplier);

            SaveConfig();
        }

        private void UpdateIndividualItemStackSize(int itemId, int stackLimit)
        {
            ItemDefinition item = ItemManager.FindItemDefinition(itemId);

            if (_config.IndividualItemStackSize.ContainsKey(item.shortname))
            {
                _config.IndividualItemStackSize[item.shortname] = stackLimit;

                SaveConfig();

                return;
            }

            _config.IndividualItemStackSize.Add(item.shortname, stackLimit);

            SaveConfig();
        }

        private void UpdateIndividualItemStackSize(string shortname, int stackLimit)
        {
            if (_config.IndividualItemStackSize.ContainsKey(shortname))
            {
                _config.IndividualItemStackSize[shortname] = stackLimit;

                SaveConfig();

                return;
            }

            _config.IndividualItemStackSize.Add(shortname, stackLimit);

            SaveConfig();
        }

        private void PopulateIndividualItemStackSize()
        {
            if (_config.IndividualItemStackSize.Count == 0)
            {
                Log($"Populating Individual Item Stack Sizes in configuration.");

                _config.IndividualItemStackSize = _vanillaDefaults;
            }
            else
            {
                foreach (ItemDefinition itemDefinition in ItemManager.GetItemDefinitions())
                {
                    if (!_config.IndividualItemStackSize.ContainsKey(itemDefinition.shortname))
                    {
                        Log($"Adding new item {itemDefinition.shortname} to IndividualItemStackSize in configuration.");

                        _config.IndividualItemStackSize.Add(itemDefinition.shortname, itemDefinition.stackable);
                    }
                }
            }

            SaveConfig();
        }

        #endregion

        #region Localization

        protected override void LoadDefaultMessages()
        {
            lang.RegisterMessages(new Dictionary<string, string>
            {
                ["NotEnoughArguments"] = "This command requires {0} arguments.",
                ["InvalidItemShortnameOrId"] =
                    "Item shortname or id is incorrect. Try stacksizecontroller.itemsearch [partial item name]",
                ["InvalidCategory"] = "Category not found. Try stacksizecontroller.listcategories",
                ["OperationSuccessful"] = "Operation completed successfully.",
            }, this);
        }

        private string GetMessage(string key)
        {
            return lang.GetMessage(key, this);
        }

        private string GetMessage(string key, string playerId)
        {
            if (_config.HidePrefixWithPluginNameInMessages || playerId == "server_console")
            {
                return lang.GetMessage(key, this, playerId);
            }

            return $"<color=#ff760d><b>[{nameof(StackSizeController)}]</b></color> " +
                   lang.GetMessage(key, this, playerId);
        }

        #endregion

        #region Hooks

        // Credit to WhiteThunder- https://github.com/AnExiledDev/StackSizeController/pull/7
        // Fix initial fuel amount for vendor-spawned helis since they use 20% of max stack size of low grade.
        private void OnEntitySpawned(MiniCopter heli)
        {
            // Ignore if a known plugin is loaded that adjusts heli fuel.
            if (AirFuel != null || GetToDaChoppa != null || VehicleVendorOptions != null)
                return;

            // Must delay for vendor-spawned helis since the creatorEntity is set after spawn.
            NextTick(() =>
            {
                if (heli == null
                    // Make sure it's a vendor-spawned heli.
                    || !heli.IsSafe()
                    // Make sure the game hasn't changed unexpectedly.
                    || heli.StartingFuelUnits() != -1)
                    return;

                var fuelItem = heli.GetFuelSystem()?.GetFuelItem();
                if (fuelItem == null
                    // Ignore other types of fuel since they will have been placed by mods.
                    || fuelItem.info.shortname != "lowgradefuel"
                    // Ignore if the fuel amount is unexpected, since a mod likely adjusted it.
                    || fuelItem.amount != fuelItem.info.stackable / 5)
                    return;

                var hookResult = Interface.CallHook("OnVendorHeliFuelAdjust", heli);
                if (hookResult is bool && (bool)hookResult == false)
                    return;

                fuelItem.amount = 100;
                fuelItem.MarkDirty();
            });
        }

        int OnMaxStackable(Item item)
        {
            if (_vanillaDefaults == null)
            {
                return item.info.stackable;
            }

            return GetStackSize(item.info);
        }

        #endregion

        #region Commands

        private void SetStackCommand(IPlayer player, string command, string[] args)
        {
            if (args.Length != 2)
            {
                player.Reply(
                    string.Format(GetMessage("NotEnoughArguments", player.Id), 2));

                return;
            }

            ItemDefinition itemDefinition = ItemManager.FindItemDefinition(args[0]);
            string stackSizeString = args[1];

            if (itemDefinition == null)
            {
                player.Reply(GetMessage("InvalidItemShortnameOrId", player.Id));

                return;
            }

            if (stackSizeString.Substring(stackSizeString.Length - 1) == "x")
            {
                UpdateIndividualItemStackMultiplier(itemDefinition.itemid,
                    Convert.ToSingle(stackSizeString.TrimEnd('x')));
                SetStackSizes();
                player.Reply(GetMessage("OperationSuccessful", player.Id));

                return;
            }

            UpdateIndividualItemStackSize(itemDefinition.shortname, Convert.ToInt32(stackSizeString.TrimEnd('x')));

            SetStackSizes();

            player.Reply(GetMessage("OperationSuccessful", player.Id));
        }

        private void SetAllStacksCommand(IPlayer player, string command, string[] args)
        {
            if (args.Length != 1)
            {
                player.Reply(
                    string.Format(GetMessage("NotEnoughArguments", player.Id), 1));
            }

            foreach (string category in _config.CategoryStackMultipliers.Keys.ToList())
            {
                _config.CategoryStackMultipliers[category] = Convert.ToInt32(args[0]);
            }

            SaveConfig();
            SetStackSizes();

            player.Reply(GetMessage("OperationSuccessful", player.Id));
        }

        private void SetStackCategoryCommand(IPlayer player, string command, string[] args)
        {
            if (args.Length != 2)
            {
                player.Reply(
                    string.Format(GetMessage("NotEnoughArguments", player.Id), 2));
            }

            ItemCategory itemCategory = (ItemCategory)Enum.Parse(typeof(ItemCategory), args[0], true);

            _config.CategoryStackMultipliers[itemCategory.ToString()] = Convert.ToInt32(args[1].TrimEnd('x'));

            SaveConfig();
            SetStackSizes();

            player.Reply(GetMessage("OperationSuccessful", player.Id));
        }

        private void ItemSearchCommand(IPlayer player, string command, string[] args)
        {
            if (args.Length != 1)
            {
                player.Reply(
                    string.Format(GetMessage("NotEnoughArguments", player.Id), 1));
            }

            List<ItemDefinition> itemDefinitions = ItemManager.itemList.Where(itemDefinition =>
                    itemDefinition.displayName.english.Contains(args[0]) ||
                    itemDefinition.displayDescription.english.Contains(args[0]) ||
                    itemDefinition.shortname.Equals(args[0]) ||
                    itemDefinition.shortname.Contains(args[0]))
                .ToList();

            TextTable output = new TextTable();
            output.AddColumns("Unique Id", "Shortname", "Category", "Vanilla Stack", "Custom Stack");

            foreach (ItemDefinition itemDefinition in itemDefinitions)
            {
                output.AddRow(itemDefinition.itemid.ToString(), itemDefinition.shortname,
                    itemDefinition.category.ToString(), _vanillaDefaults[itemDefinition.shortname].ToString("N0"),
                    Mathf.Clamp(GetStackSize(itemDefinition), 0, int.MaxValue).ToString("N0"));
            }

            player.Reply(output.ToString());
        }

        private void ListCategoriesCommand(IPlayer player, string command, string[] args)
        {
            TextTable output = new TextTable();
            output.AddColumns("Category Name", "Items In Category");

            foreach (string category in Enum.GetNames(typeof(ItemCategory)))
            {
                output.AddRow(category, ItemManager.itemList.Where(x => x.category.ToString() == category).Count().ToString());
            }

            player.Reply(output.ToString());
        }

        private void ListCategoryItemsCommand(IPlayer player, string command, string[] args)
        {
            if (args.Length != 1)
            {
                player.Reply(string.Format(GetMessage("NotEnoughArguments", player.Id), 1));
            }

            ItemCategory itemCategory = (ItemCategory)Enum.Parse(typeof(ItemCategory), args[0]);

            TextTable output = new TextTable();
            output.AddColumns("Unique Id", "Shortname", "Category", "Vanilla Stack", "Custom Stack", "Multiplier");

            foreach (ItemDefinition itemDefinition in ItemManager.GetItemDefinitions()
                .Where(itemDefinition => itemDefinition.category == itemCategory))
            {
                output.AddRow(itemDefinition.itemid.ToString(), itemDefinition.shortname,
                    itemDefinition.category.ToString(), _vanillaDefaults[itemDefinition.shortname].ToString("N0"),
                    Mathf.Clamp(GetStackSize(itemDefinition), 0, int.MaxValue).ToString("N0"),
                    _config.CategoryStackMultipliers[itemDefinition.category.ToString()].ToString());
            }

            player.Reply(output.ToString());
        }

        #endregion

        #region Dev Use

        private void GenerateVanillaStackSizeFileCommand(IPlayer player, string command, string[] args)
        {
            GenerateVanillaStackSizeFile();
        }

        private void GenerateVanillaStackSizeFile()
        {
            RevertStackSizes();

            SortedDictionary<string, int> vanillaStackSizes = new SortedDictionary<string, int>();

            foreach (ItemDefinition itemDefinition in ItemManager.GetItemDefinitions())
            {
                vanillaStackSizes.Add(itemDefinition.shortname, itemDefinition.stackable);
            }

            Interface.Oxide.DataFileSystem.WriteObject(nameof(StackSizeController) + "_vanilla-defaults",
                vanillaStackSizes);

            SetStackSizes();

            Log("Vanilla stack sizes file updated. Custom stack sizes restored.");
        }

        #endregion

        #region Helpers

        private void DownloadVanillaDefaults()
        {
            Log($"Acquiring vanilla defaults file from official GitHub repo and overwriting; {_vanillaDefaultsUri}");

            try
            {
                webrequest.Enqueue(_vanillaDefaultsUri, null, SetVanillaDefaults, this, RequestMethod.GET);
            }
            catch (Exception ex)
            {
                LogError($"Exception encountered while attempting to get vanilla defaults: {ex}");
            }
        }

        private void SetVanillaDefaults(int code, string response)
        {
            if (code != 200 || response == null)
            {
                LogWarning($"Unable to get result from GitHub, code {code}. If you don't have a vanilla defaults datafile, the plugin will throw errors. " +
                    $"Reloading should resolve this unless there is something preventing downloads from external sites.");
                LogWarning("If the issue persists, check the uMod forums for StackSizeController for a manual fix.");

                return;
            }

            _vanillaDefaults = JsonConvert.DeserializeObject<Dictionary<string, int>>(response);

            Interface.Oxide.DataFileSystem.WriteObject(nameof(StackSizeController) +
                    "_vanilla-defaults", _vanillaDefaults);

            // TODO: Consider refactoring workflow to avoid ambiguity
            PopulateIndividualItemStackSize();
            SetStackSizes();
        }

        private int GetVanillaStackSize(ItemDefinition itemDefinition)
        {
            return _vanillaDefaults.ContainsKey(itemDefinition.shortname)
                ? _vanillaDefaults[itemDefinition.shortname]
                : itemDefinition.stackable;
        }

        private int GetStackSize(int itemId)
        {
            return GetStackSize(ItemManager.FindItemDefinition(itemId));
        }

        private int GetStackSize(ItemDefinition itemDefinition)
        {
            try
            {
                if (_ignoreList.Contains(itemDefinition.shortname))
                {
                    return GetVanillaStackSize(itemDefinition);
                }

                int stackable = GetVanillaStackSize(itemDefinition);

                // Individual Limit set by shortname
                if (_config.IndividualItemStackSize.ContainsKey(itemDefinition.shortname))
                {
                    stackable = _config.IndividualItemStackSize[itemDefinition.shortname];
                }

                // Individual Multiplier set by shortname
                if (_config.IndividualItemStackMultipliers.ContainsKey(itemDefinition.shortname))
                {
                    return Mathf.RoundToInt(stackable * _config.IndividualItemStackMultipliers[itemDefinition.shortname]);
                }

                // Individual Multiplier set by item id
                if (_config.IndividualItemStackMultipliers.ContainsKey(itemDefinition.itemid.ToString()))
                {
                    return Mathf.RoundToInt(stackable * _config.IndividualItemStackMultipliers[itemDefinition.itemid.ToString()]);
                }

                // Category stack multiplier defined
                if (_config.CategoryStackMultipliers.ContainsKey(itemDefinition.category.ToString()) &&
                    _config.CategoryStackMultipliers[itemDefinition.category.ToString()] > 1.0f)
                {
                    return Mathf.RoundToInt(
                        stackable * _config.CategoryStackMultipliers[itemDefinition.category.ToString()]);
                }

                return Mathf.RoundToInt(stackable * _config.GlobalStackMultiplier);
            }
            catch (Exception ex)
            {
                LogError("Exception encountered during GetStackSize. Item: " + itemDefinition.shortname + " Ex:" + ex.ToString());

                return GetVanillaStackSize(itemDefinition);
            }
        }

        private void SetStackSizes()
        {
            foreach (ItemDefinition itemDefinition in ItemManager.GetItemDefinitions())
            {
                if (itemDefinition.condition.enabled && !_config.AllowStackingItemsWithDurability)
                {
                    itemDefinition.stackable = Mathf.Clamp(GetVanillaStackSize(itemDefinition), 1, int.MaxValue);

                    continue;
                }

                if (_ignoreList.Contains(itemDefinition.shortname))
                {
                    continue;
                }

                itemDefinition.stackable = Mathf.Clamp(GetStackSize(itemDefinition), 1, int.MaxValue);
            }
        }

        private void RevertStackSizes()
        {
            Log("Reverting stack sizes to vanilla defaults.");

            foreach (ItemDefinition itemDefinition in ItemManager.GetItemDefinitions())
            {
                if (itemDefinition.condition.enabled && !_config.AllowStackingItemsWithDurability)
                {
                    continue;
                }

                if (_ignoreList.Contains(itemDefinition.shortname))
                {
                    continue;
                }

                itemDefinition.stackable = Mathf.Clamp(GetVanillaStackSize(itemDefinition), 1, int.MaxValue);
            }
        }

        #endregion
    }​

I know some C#, but am not proficient enough to immediately see an issue or really an obvious place to start looking for the likely cause, but will attempt to resolve the issue and post an update if successful.