I’ve managed to fix this issue but thought it wise to post here in case anyone else hits this problem.
I have a AI Controller that hooks up to the Game Mode on Possess and gets some level wide managers for coordinating. Problem I was hitting was the asset thumbnail render in the content browser was crashing out the editor.
Root cause was that the thumbnail render spawns a pawn and even goes as far as spawning a controller to possesses the pawn in the content browser. Is this expected behaviour?
The fix I have is that check the return of world->GetAuthGameMode - this is null in the content browser spawn so you can prevent any potentially dangerous accesses.