I had this happen a lot. Would go to place another painting in the area and it wouldn't let me, as if the painting was there, I just couldn't see it.
Did this by accident and it brought the painting back up, don't know if it was a fluke or what. Do the walls as cutaway, then raise them back up for the whole wall to be there.
My paintings showed up on the walls.
Don't know why, the walls had all been up, but for some reason they didn't show up.
I had given up on them, figured they were gone forever and just dropped the walls to see into the other rooms, I prefer to play with them down. When I brought them back up to take a photo and didn't want the other room to show up (bathroom), the paintings were there on the wall. All of the ones that I had put there and had vanished were now on the wall.
Give that a try and see if it brings them back up. Hope it helps