this was showing when server started up 

Failed to call hook 'OnServerInitialized' on plugin 'StackSizeController v2.0.0' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.StackSizeController.DetermineStack (ItemDefinition item) [0x00047] in <7bd8c51154b64ba4b3c3109614e3bcfe>:0 
  at Oxide.Plugins.StackSizeController.UpdateItems () [0x0003a] in <7bd8c51154b64ba4b3c3109614e3bcfe>:0 
  at Oxide.Plugins.StackSizeController.OnServerInitialized () [0x0000c] in <7bd8c51154b64ba4b3c3109614e3bcfe>:0 
  at Oxide.Plugins.StackSizeController.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x0037e] in <7bd8c51154b64ba4b3c3109614e3bcfe>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <9affce1cd15c4ec183941adef8db1722>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <4452f821def6406d834e4149849fe7ea>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <4452f821def6406d834e4149849fe7ea>:0 ​

did u delete your old config before updating to new version ?

i did delete ang got small stacks even i have all to 9 millions in config

i'm a goof i downloaded the new file but failed to transfer it over to my linux box deleted the plugin and config and readded it seems to be working right now my stacks are stacking 
@PlayerKnownAsRay don't forget to run command again 

Chat Commands
/stack <item.short.name> <stack size> -- Set the stack size of item to specified amount (ex: /stack ammo.rocket.hv 64)
/stackall <stack size> -- Set the stack size of all items to specified amount (ex: /stack 65000)

or 
Console command "stack" and "stackall" also work same way as the chat commands above.​

thanks, works now!