I spent some time making custom button widgets that could be used in separate widgets like the Main menu and the Pause menu, and had a few variables exposed to instances like font size and colour. Is this the type of thing you mean when you say inheritance structure? I deleted the event dispatchers I was using and simplified my UI, but am still getting crashes.
I find it odd that I can load the level in Play mode, but not in Editor mode. I can access and play the levels when accessed through the game, but I cannot open them to edit, because UE crashes.