You are correct, this is an issue with one of the motors. Which direction is the chair spinning in?

I had the same problem. There are circuit breakers under my seat, one of them had opened. (It was a push button type and was popped out further than the other.) Under the seat, near where the cables all connect. All I had to do was reset the breaker. I know what caused it. I was making a tight turn, and one tire was very low and over loaded the motor.