Hi!
I would say if it’s just a single pickup shaft spin during certain period of time - and you having problem with second paper being picked up - that could be separation pad that is worn (and should be replaced), but if that shaft spinning twice during one pickup cycle and that is causing double pickup - that’s issue with solenoid (foam pad it’s not good in there and could be replaced with 2 cut pieces of any duct tape).
Good luck!