No neighbors in the apartment

Hiii,

Since the last update, every time I move my Sims into an apartment, new neighbors appear. However, after about a day in-game, they disappear. When I try to click on their apartments, there are no interaction options. The other apartments seem completely empty, which makes the game feel a bit boring. Does anyone know how to fix this? I do play with some mods, but I didn’t have this issue before the latest update.