You mentioned freshly mopped? Ever see water move something - its a stretch but water got under it and it moved. Ever sit a a plate on a table and there is a little water and it just moves sideways? Same concept, larger items perhaps?
I'll throw this in the mix.
Death Valley Sailing Stones Caught in Action for First Time | Physics | Sci-News.com
The fresh mopping would be something that changed the norm is what I would try to connect.
Put it back as it was, and set up a game camera to see if it moves on its own, again.