This has been happening for me as well, since Sept 2. I tried to play a game that last saved fine on Aug 29 and it's not saving changes, even using Save As and trying to create a copy of the file leaves it with the same content as Aug 29m even though the file itself says it was last saved later on.
I don't know what triggered this. I started a new file Sept 3 and (fingers crossed) so far it seems to be doing okay and saved after a couple times opening and closing. But now I'm afraid to open any of my older files because if this is a corruption issue, I don't want it affecting my legacy files, etc. t
The file that won't save anymore is a new one I started after getting Lovestruck on release day, and the only thing I can think of that's different in this file from other saves I have is that it has a lot of Sims downloaded from Cupid's Corner, so my total number of Sims added to the game is 64/150, which is pretty high for me and the file size I've noticed is VERY large compared to all my other saves (even my longtime legacy), but other than that, nothing weird happened while I was playing. No error messages. It just won't save any progress I make anymore. It keeps going back to the same Sim day/time. Recovering the save doesn't change anything, and repairing the game didn't fix it either. 🤔