Apparently it is possible for rides to get stuck upside down: https://www.cbsnews.com/pittsburgh/news/kennywood-aero-360-still-closed-stuck-upside-down/

I am familiar with how the frisbee rides get stuck upside down I would assume this would be similar.  The motor turns off as the arm approaches the top and the control system waits until the arm reaches a set point before reengaging the motor, so it is just coasting over the top.  It would be very easy to produce too strong of forces if the motor was engaged at all times.

In a case like this a gust of wind or something else at just the right or for the riders wrong moment provides enough resistance the ride vehicle balances upside down. The ride system does not see the motion it is expecting so it faults and turns off power to the motor.  On frisbee rides like the ones from SBF Visa when wind does eventually push the ride vehicle over since the ride faulted the motor will not engage to slow the arm, and it just swings back and forth for a long time before it stops allowing the ride op to release the passengers.