My levels deleted itselves somehow, everyday!

There is no reason for that but my levels delete itselves somehow everyday. I lost lots of hours beacuse of that!!
Please help me with this. I have no idea.

I have recently run into the same problem, very infuriating. After starting UE4 it gave me a log error saying it couldnt export(?) outer assets pertaining to my character mesh BP but it also deleted my whole level… WTF?