This is all a bit odd, but if the chain was moving without issue in the other part of the stroke, I would say that this issue is probably not the pully wheels, but somewhere else in the system that would cause the stoppaged. Two things that come to mind are that possibly the crank was hitting the front derailleur, or that their is a frozen link in the chaing that is causing a kink that stops the chain from moving through the rear derailleur.