In my experience there are quite a few things that can cause this. I spent about two days locating a single collapsed graph which caused crashes moving from 4.12 to 4.14 (I think). The crash was caused even by loading a BP which simply referenced the offending BP in a variable.
Also - I had a similar problem where I’d been experimenting with a plugin which had it’s own variable class, and when I disabled the plugin it caused problems because I still had the variables in the BP.