a week ago
This just happened to me as well, and I was just visiting another apartment, not playing the paranormal career, I played it with another sim earlier but now when I am just visiting another apartment with another sim which is not in the career the door is missing and I can't knock on the door.
Every apartment has no door to knock on. I can't get them to come back when I click on the walls view. The only way i can complete the task is to preform a ritual in the hallway. If the doll or ghosts are in the hallway I can do something with them. The door to the other apartment is there, just not the one I was sent too.
The best I've been able to get around this is create a seance circle and preform ceremony over and over.