While building their robot, two of the motors belonging to a team from my school somehow managed to get completely stuck so that they could not turn at all.
The motors had been used before and had worked fine but when connected to the brain to run them, they did not move and drew the stall current of 2A and the shafts of the motors could not be turned by hand even when disconnected from the brain.
I fully disassembled one of the motors and found that the actual motor was stuck but when I twisted it with significant force, it became unstuck and worked fine when the brain was connected.
The other motor I managed to get unstuck by twisting hard with a gear on high strength shaft in a 600rpm cartridge.
Has anyone else had similar problems of motors getting stuck?