@puzzlezaddict Thanks for the reply! Since looking more at my game, I've also noticed that when I'm actually on a lot, all the lots around me appear as they would when I first got the game. The ones that are originally blank are blank, and the ones that have EA houses on them have EA houses (when I look at them from a different lot, when I actually go to the lot even the EA hosues disappear). Everything looks like it should on the map, though.
To answer your questions, when I travel with the sims, nothing on any lot I go to (the park, houses I've built, EA houses... anything) shows up. When I go back to the home lot, there's still nothing there.
When I attempt to save a lot, the gallery shows that nothing is there and that the lot is worth zero simoleons.
How would I recover a backup save?
Thanks again for our help!