Considering how the mouth looks it still appears to be in good shape. My only guess is that something on the rock the foot is attached to is irritating it, perhaps a Vermitid Snail or something like that. When they split they usually first develop multiple mouths.
I don't see any reason not to cut it off the rock and reattach it to a new rock. If you don't pull off all of the foot a couple/few new Yumas should grow from whatever you leave behind.