The builds I do are not saving. Houses I download from the gallery disappear too. The game itself saves, just not any houses I create, or download into the game save at all.
Not sure if this will work for you, But for me I had the same problem. I would load an older save to play and show up to an empty lot, and my library missing the build as well like it did not exist, even though I know for sure I had saved them to my library, not only once but several times just to make sure. I kept trying to figure it out, I thought to myself what is different from now to then? I remember that I have purchase a few more game packs and unticked the newer packs and they then showed up in my library. Thank God ! Some of the build I had lost took me hours to build. I am so happy I was able to figure it out. I hope this helps you as well. Good luck.
