Received this error on both my servers when restarting them for the newest hotfixes from Facepunch.

13:57 [Error] Failed to call hook 'Unload' on plugin 'StackModifier v2.0.0' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.StackModifier.ResetStacks () [0x0007b] in <930172221f7a445fa8828adeb455ae49>:0

  at Oxide.Plugins.StackModifier.Unload () [0x00010] in <930172221f7a445fa8828adeb455ae49>:0

  at Oxide.Plugins.StackModifier.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00582] in <930172221f7a445fa8828adeb455ae49>:0

  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <23ba99f131254889867c71f0bd137b1d>:0

  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <157a94ee66ab4a7991faecd1eb84be3b>:0

  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <157a94ee66ab4a7991faecd1eb84be3b>:0

I cannot recreate that problem with the latest 2x update on umod. 

That could only happen if the plugin was either modified or you have a version from somewhere else maybe ?

Must have been a "hiccup". I noticed it when it happened, but nothing was going wrong with it. So, I just posted it here, just in case. It's the official one from Umod. All seems to be fine now. Thanks for looking into it anyway!