Hi Hort
I looked at your animations again and I think that they are actually showing that the leg is rising slightly out of the soil. Perhaps that leg is moving up while the other legs, resing on the ice, are settling in the ice.
I did'nt notice that before as well as the significant movement of small particles (pebbles) around the leg saucer.
It looks as if your deduction of the legs slipping/settling was, as usual, a good call.
Winston