Hi there, i’m not an expert on this one but i hope i can help^^
It seems to me the engine found something invalid on your project, it can be an material,mesh, an invalid location… etc.
You already tried to validate the assets of your project or fix the redirectors? I had the same problem sometime ago and it was fixed after i validated everything.
If you never did that it’s very simple: Right click on the CONTENT folder and select “Fix Up Redirectors in Folder”. When finished, try the option “Validate Assets in Folder”. Both operations can take sometime and i recommend you do a backup first just for safety^^ (I never had any problems, but it’s just for safety)