J4 stepper motor

Thought to reach out here (also raised a ticket with Stepper Online which is ongoing) as I am having trouble with the J4 motor. It simply does not rotate neither through the software nor manually. It does merely vibrate a little when trying to jog. I did the troubleshooting during the commissioning trials and had the robot in front of a monitor and only then noticed these gaps in the motor housing. Anyone come across this? Is this normal (which I doubt it is...)? Many thanks!