Prop Spins Intermittently while other props spin perfectly

Drone Issue:Props spins and after remotely stopping all props, the rear right prop will sometimes not spin unless you give it a push. I carefully removed the cover revealing gears and saw nothing unusual. I tested the shaft by starting props and the shaft in question does not spin on its own. If you turn it the shaft will spin again and MAY behave fine for two or three test but eventually it will require that you spin shaft manually to get the shaft spinning. Is this a loose wire problem? Thanks for any suggestions.