Since Update I got this:

Failed to call hook 'CanStackItem' on plugin 'CustomSkinsStacksFix v1.0.4' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.CustomSkinsStacksFix.CanStackItem (Item original, Item target) [0x0000d] in <c4fccfa2a2f94b4d864dcc31a2ab9f16>:0
  at Oxide.Plugins.CustomSkinsStacksFix.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00083] in <c4fccfa2a2f94b4d864dcc31a2ab9f16>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <60c318df79ed41688ea59335e48d61ad>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <50629aa0e75d4126b345d8d9d64da28d>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <50629aa0e75d4126b345d8d9d64da28d>:0​

Running Stack Size Controller?

Yes indeed

Delete this plugin. Its function is being duplicated by Stack Size Controller, and it's conflicting. Think two guys looking down a hole at the same time and bumping heads. Since this plugin is limited and its sole function is duplicated by SSC, it's best to just not use this one.