It sounds like the “lip” or hook does not stick into the barrel far enough, or, the spring isn’t curved properly to allow it to fit tight against the barrel. The hook should stick down into the barrel far enough for the spring to hook on it preventing it from turning or slipping. Schatz barrels are hard to come by, you might need to take the one you have to a good clockmaker and have it repaired.
Art Fish
Back In Time Clock Repair