frbch This issue is sometimes caused or exacerbated by mods and custom content, so please remove your Mods folder and see whether you still can't save. You can use "save as" rather than "save" so you don't overwrite your progress.
Please also let me know whether OneDrive is running on this computer, even if you never use it.
Separately, what do you mean by letting your computer sleep a little? Are you restarting the computer after you close the game, or at least before the next time you play? Not doing so can cause various issues that masquerade as something else, so it's always helpful to restart your computer frequently while troubleshooting.