In my case, I found that all the widgets had circular references between themselves and my player controller (the PC created the widget, and then i had button clicked handlers in the widget that got the player controller and cast it to the blueprint type that was creating the widget in the first place). I suspected these were the cause, so I removed the circular references, and it fixed the crash.
I replaced that behaviour with an event driven system, so the widget doesn’t reference the player controller any more, but instead uses and event dispatcher which the PC handles.