I don't think there was a malfunction of any kind. I am willing to bed that the rider (Rosy) pulled the restraint down against her stomach, not her waist. I don't think she was ever safely secured. Then on that first turn, she slipped out. At SFOT, Batman The Ride used to have a test seat. I feel like that would make sense for every ride. Put a test seat near the entrance of every rollercoaster and have someone on staff in charge of making sure everyone is safe to ride before they get in line.