Yeah this is a very consistent problem. I just moved my treasures to a new location and they have sunk again
Here is a picture from the same treasure room the previous evening, before I logged off. You can see the two treasure chests and the lemurian statue which have vanished in todays picture. The cat next to the bookkeeper has sunk into the foundation in todays picture.
Its 100% a bug, but we can only hope devs are able to fix it.