This is in the error reporting plugin report: 
"Furnace Splitter: Forced Unloaded
Due to excessive error spams discord error logger has forced unloaded this plugin.
Total Errors: 46x
Open a support ticket"

Really needs an update.

The specific errors: 

Failed to call hook 'OnTick' on plugin 'FurnaceSplitter v2.5.3' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.FurnaceSplitter.GetOvenInfo (BaseOven oven) [0x0002a] in <73eaab3967994f88a9b7bb97dac04592>:0

  at Oxide.Plugins.FurnaceSplitter.OnTick () [0x0003a] in <73eaab3967994f88a9b7bb97dac04592>:0

  at Oxide.Plugins.FurnaceSplitter.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x002a7] in <73eaab3967994f88a9b7bb97dac04592>:0

  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <42f9bedc659b4f4786eb778d3cd58968>:0

  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000de] in <15f61ddda771464d8246ebdce8ff4811>:0

  at (wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition.Oxide.Core.Plugins.Plugin.CallHook_Patch0(Oxide.Core.Plugins.Plugin,string,object[])

Failed to call hook 'CanMoveItem' on plugin 'FurnaceSplitter v2.5.3' (NullReferenceException: Object reference not set to an instance of an object)
Same

at Oxide.Plugins.FurnaceSplitter.GetOvenInfo (BaseOven oven) [0x0002a] in <1c6c025834ee403f9a3d3fcd0445e8cf>:0
at Oxide.Plugins.FurnaceSplitter.AutoAddFuel (PlayerInventory playerInventory, BaseOven oven) [0x0000d] in <1c6c025834ee403f9a3d3fcd0445e8cf>:0
at Oxide.Plugins.FurnaceSplitter.CanMoveItem (Item item, PlayerInventory inventory, ItemContainerId targetContainerId, System.Int32 targetSlotIndex, System.Int32 splitAmount) [0x001b8] in <1c6c025834ee403f9a3d3fcd0445e8cf>:0
at Oxide.Plugins.FurnaceSplitter.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x008a5] in <1c6c025834ee403f9a3d3fcd0445e8cf>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <42f9bedc659b4f4786eb778d3cd58968>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000de] in <15f61ddda771464d8246ebdce8ff4811>:0
at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <15f61ddda771464d8246ebdce8ff4811>:0

I also have this issue

same here

yep same issue here. right clicking ore into electric furnaces also ends up duplicating the ore

I think it happens when you have all in config like:

"*": {
"enabled": true,
"fuelMultiplier": 1.0
},

Or if you enable the apartment. Disabling apartments probably fixes it w/o all, but if you use all (*), you can use this temporary measure to stop the errors (search for //trader):

        private void OnTick()
        {
            while (queuedUiUpdates.Count > 0)
            {
                BaseOven oven = queuedUiUpdates.Pop();

                if (!oven || oven.IsDestroyed)
                    continue;

                OvenInfo ovenInfo = GetOvenInfo(oven);
                
                if (ovenInfo == null) //trader apartments added
                    continue;

                GetLooters(oven)?.ForEach(player =>
                {
                    if (player != null && !player.IsDestroyed && HasPermission(player) && GetEnabled(player))
                    {
                        CreateUi(player, oven, ovenInfo);
                    }
                });
            }
        }

        //Trader apartments
        public OvenInfo GetOvenInfo(BaseOven oven)
        {
            if (oven == null || oven.IsDestroyed)
                return null;
        
            if (oven.fuelType == null)
                return null;
        
            var burnable = oven.fuelType.GetComponent<ItemModBurnable>();
            if (burnable == null)
                return null;
        
            OvenInfo result = new OvenInfo();
        
            PluginConfig.OvenConfig ovenCfg = GetOvenConfig(oven.ShortPrefabName);
            float fuelMultiplier = ovenCfg?.fuelMultiplier ?? 1f;
        
            float ETA = GetTotalSmeltTime(oven) / oven.smeltSpeed;
            float fuelUnits = burnable.fuelAmount;
            float neededFuel = (float)Math.Ceiling(ETA * (oven.cookingTemperature / 200f) / fuelUnits);
        
            result.FuelNeeded = neededFuel * fuelMultiplier;
            result.ETA = ETA;
        
            return result;
        }
        /*public OvenInfo GetOvenInfo(BaseOven oven)
        {
            OvenInfo result = new OvenInfo();
            PluginConfig.OvenConfig ovenCfg = GetOvenConfig(oven.ShortPrefabName);
            float fuelMultiplier = ovenCfg != null ? ovenCfg.fuelMultiplier : 1.0f;
            float ETA = GetTotalSmeltTime(oven) / oven.smeltSpeed;
            float fuelUnits = oven.fuelType.GetComponent<ItemModBurnable>().fuelAmount;
            float neededFuel = (float)Math.Ceiling(ETA * (oven.cookingTemperature / 200.0f) / fuelUnits);

            result.FuelNeeded = neededFuel * fuelMultiplier;
            result.ETA = ETA;

            return result;
        }*/

Then at the start of AutoAddFuel:

        private void AutoAddFuel(PlayerInventory playerInventory, BaseOven oven)
        {
            //trader apartments mod starts
            var ovenInfo = GetOvenInfo(oven);
            if (ovenInfo == null)
                return;
            
            int neededFuel = (int)Math.Ceiling(ovenInfo.FuelNeeded);
            //trader int neededFuel = (int)Math.Ceiling(GetOvenInfo(oven).FuelNeeded);
            //trader apartments mod ends
            neededFuel -= oven.inventory.GetAmount(oven.fuelType.itemid, false);