While trying to sort out the stiff wheel bearing challenge, one symptom of this was when freewheeling, the chain would skip off the smallest cog. Obviously not good, but when pedalling it doesn't skip. Is this just down to the abnormal freewheel sticking (which I think I've solved), or a sign of a worm cog? It doesn't look worn, no hooked teeth, burrs or pointy teeth, it looks fine. It's a new chain on a used cassette.