I don't have any aircraft specific knowledge but issues related to the stoppage/turning off of an electric motor are generally associated with the failure of the 'freewheel diode' that's part of the motor (or motor drive, in larger installations) and is there to stop transient overvoltage spikes by allowing the collapsing magnetic field to dissipate the electrical energy it generates into a loop rather than slamming up against an open circuit. (It's there to prevent the electrical version of water hammer.)
Googling that term (freewheel diode) and a bit of looking at the wiring diagram might help you out. Diodes can be tested with a multimeter. It may be part of the motor assembly or inside the motor.
Failing that, yes, voltage regulator failure, they do get old and fail...