I don't really know why it happens, but this has happened since I started playing the sims. The doormat on most of the apartmentdoors just turns pitch black in live mode.
I'm having a very similar issue except both furniture and sims within the apartment seems to glitch out too. It's never the apartment of the family I'm playing, and it's usually only one apartment on the lot.
If my sims go inside the apartment to visit the neighbor, they become blacked out. I can still have my sims interact with objects and other sims within the apartment. If my playable sims or the NPCs leave the apartment, they return to normal.
I didn't have this issue until I recently did a fresh reinstall of the game. I do have some mods, but they didn't cause this issue until I completed the reinstall.