I had this 3 times in a row in another building to. I currently don't want to keep testing as long as this bug is present. I think this is based on server lag. Maybe a more client side system and engine that would check if these movements are legit to prevent speed hacks would be much better.
The movement system should be more client side then server side the only thing the server should do is check if movement is legit to prevent speedhacking.
Apparently the server doesn't even have to lag to encounter this problem. If fell through the floor on a third floor apartment pressing ESC just showed the buildings near it but the building i was in was invisible. This bug is getting Urgent!