
I am not a vet, but hopping/skipping can be patella luxation, especially if the lameness is sudden and “fixes” itself suddenly too.
My papillon has low grade PL and when a kneecap moves out of place he squeals, it’s obviously uncomfortable. It usually goes back in almost immediately by itself (I’ve helped a couple of times) and he’s absolutely back to normal after a minute’s rest, with no sign of lameness or pain once it’s in place again.
I’d get your vet to have a look, whatever it is you’re best off knowing about it I think. Not trying to scare you or anything, but we can’t diagnose anything on an Internet forum.