What’s happened is something inside the internal motor worked its way to a place it’s not supposed to be.
It happened to several of our motors last season.
While you can dislodge whatever’s jamming it, it may or may not work, and even then it is at very high risk of jamming again so I wouldn’t recommend using it.
If you can’t get a free replacement from VEX, you can swap the internal motor with another motor that has a fried board, so that one of them works and the other is just more dead.
The board has pins that stick into little sockets on the motor, and you can easily separate them.