Having the same issue. About to give up on playing until I see a fix.
edit - it is definitely avast antivirus for me. I turned it off for 5 minutes and the problem went away. Obviously, Im not going to play without my antivirus enabled, so it still needs to be fixed - just adding context if the devs are reading.
After reading your edit, I went into my AV and added the game to my exceptions list, and it cleared the issue out, so far. I was able to quick save, auto saves went through, and I just saved and quit with no crashes.