I didnt have this error before the update, but now after update, I get this error when shutting down the server.

Failed to call hook 'IOnServerShutdown' on plugin 'RustCore v2.0.6108' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000fb] in <18d4f19bbc844191b11ed9e69284d09b>:0

  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <18d4f19bbc844191b11ed9e69284d09b>:0

It does this even with ZERO plugins, and even 1. Last night went to bed with the server up and only 1 plugin. Woke up with a Null Reference error scrolling across my screen.
I unloaded the plugin and continued to scroll. Had to shut down the server and relaunch it. Didnt do this with prior oxide update. Not sure what changed.

Another issue since this update, plugins are not loading after restart. Oxide doesnt even load. I end up having to restart (rust server) again and the second time oxide will load with plugins. Very odd behavior. Never had this before this last update.

Have you tried reinstalling Oxide?

Yes I have quite a few times as a matter of fact. I think I may be making headway, These updates are great but they seem to be causing more problems