I want you to know that I'm not ignoring this comment (I just can't find a solution...). Historically, save problems are related to some settings that inflated the size of save files, but those issues were corrected some time ago. I've not been able to recreate this issue on my side, so I'm a bit stuck as to how to help.
That said, I have one thing we can try:
1. Open up the console (ctrl + O)
2. Type (or copy/paste): config.has_autosave = True
3. Close the console with escape
This should already be set as the default value, so I sort of expect that it won't fix the problem, but other than that I'm not sure why auto wouldn't be operating correctly.