Well this is a fun bug, and it’s so weird I don’t know if I can explain it right. I haven’t seen this one posted anywhere. I somehow manage to find the weirdest stupid bugs!
I decided to redo my library, which is made in an empty stairwell, and figured I’d attach a second empty stairwell (with a closet inbetween to avoid the known bug) on the 2nd floor of the existing library. That way if nothing I did was better than what I had, I could just keep the existing, and having it so close to the existing library made it easy to move elements I wanted to keep.
Since you know, we don’t have a save option yet.
So I got to the point where I knew I’d keep the new library, and set to moving all the attached rooms so I could delete the exiting library and put the new into place.
It all went exactly as I planned, I got almost everything put back into place, until I went to put one of the closets on the second floor (which is part of a window scene).
There is no second floor, it’s a blank void, and it shows there’s a third floor, but there’s nothing there.
I cannot select the closet I want (stored on the first floor), select the 2nd (or 3rd) floor, and move it to the spot I want on the new library’s 2nd floor; it removes the closet from my cursor, which I’ve never had an issue with before.
So many hours wasted 
There are screenshots in the reddit post I made about this in r/WoWHousing
