I have a simple mine / bomb and the actor is a destructible, if the destructible causes damage that triggers the end game event it gets corrupted, crashes the editor, and then will not let project load until it is removed.
Once the project is reloaded (after removal) then if brought back via drag and drop back into the directory it will work again until situation happens again. I have been having general troubles like this since moving to 4.18 nothing like this happened like this with previous version of the engine.
I am using the latest Nvidia drivers. The memory dump after the crash gives a memory read / write error. If it keeps happening I will turn on symbols and look into it deeper.
FIX:Right now the fix is to remove the bad BP and load the project then copy it back into the directory.