From my limited experience most of these issues occur because you did something wrong in a class’ constructor.
In Unreal constructors are used to instantiate class default objects CDO’s which do exist in the unreal editor before run-time. Basically whatever class you mark with the UCLASS() macro will have a CDO instantiated for it. Unreal simply uses the CDOs as a template to spawn in game Objects (actors, components etc). And CDOs are instantiated by using the classes’ constructors.
So if there is anything wrong with any constructor of a class marked as UCLASS() then the editor will crash at startup. And debugging it will be difficult.
Check for possible null pointer issues and access violations in class constructors.
Whenever you implement a constructor of a class make sure the game editor runs normally. That way, if it fails you can at least pinpoint the reason.