Adding my +1 vote, because I'm also having this issue with apartments that sims never lived and I never accessed from build mode. I started playing in Salim Benali's apartment in San Myshuno, then a few sim days later I went to move some sims from my library into empty apartments through the city. The game only allowed unfurnished move-ins and now the apartment interiors are wiped out from map mode.
Prior to moving in the gallery sims, I edited my apartment and the edit-able strip of land outside the apartment building (no mods and no moveobject or other build cheats when editing the outside, just placing items in the strip of edit-able tiles outside). I have City Living but not For Rent. I had no mods installed when the issue occurred but I did add mods afterward, but this all happened within a few hours of play time so I can recreate a fresh vanilla save pretty quick if necessary :)
