Diagnosis
The brushroll end caps or the motor gearbox are jammed with fine hair and debris, not the main brushroll fibers.
How to Fix It
Remove the brushroll. Use a small tool or scissors to cut and remove any hair wound tightly around the plastic end caps, especially in the deep grooves. Also, inspect the silver bearing on one end and the gear teeth on the other for obstructions.
If That Didn't Work
The brushroll motor or its sensor may be faulty. Manually spin the brushroll with your hand. It should turn freely with minimal resistance.
Heads Up
Perform this cleaning every 2-3 weeks with pet hair or long human hair. Failure to clean end caps will burn out the motor.