Just to update on this issue, I think the main problem is certain store content. Some store items have started showing up blank in the buy menu - by which I mean, I can mouse over them in the buy menu and see what they are but there is no picture, just the store icon. (It's not a question of waiting long enough for the pictures to load. They never appear.) I can buy them and they show up in game, but no matter how long I wait after purchasing, the game is unable to save after those items have been placed. This has definitely been an issue with certain dining chairs, but I noticed that there are store items in different categories (computers and some others I don't remember) that are also blank in the buy menu. I haven't tried to place those items to see if they also cause the save problem, but I have a feeling that they might.
It seems odd to me because I have a lot of living chairs from the store as well, and those all show up just fine. Again, I haven't tried placing them because I'm tired of wasting time when the game is unable to save and just sits there with the save icon endlessly spinning around. So all I know for sure is that I have store content that for some reason prevents my game from saving.