Before deleting 3-D objects, there should be a notification so that these objects are first removed from the house (so they don’t exist in the world), and then they could be permanently deleted from the game.
Right now I can only place something on top of this box to cover it.
Scary error! I think this topic should be moved to the Bug Reports category. I haven’t had such a situation. But something similar happened to me a long time ago. A downloaded item from Canvas was displaying the way it is in your picture (as a blue box). I first deleted that item in the game, and then removed it from the downloads folder. Everything went smoothly. Your situation is really scary though. I think there’s no way to get rid of this artifact. Unless you roll back to an old save where this error doesn’t exist.
Actually you could try to delete down the whole house.? You can move out of that house and relocate to another house. @dostkraut You can build a new house on the plot.
You can build a new house instead. But you need to be careful when randomly deleting things you don’t remember. Randomly deleting modded items can cause problems with your save file. This is not a bug.