Watching the video above and a couple others from the bear away, I got the impression that the capsizes were mostly due to:
1. Being overly aggressive with skipper on the wire and entering the bear away with the hull flying. With only one hull in the water you lack buoyancy up front. Having the timing of the crew going forward to hoist wrong almost looked to contribute to some.
2. Some boats had to alter their bear away to avoid another capsized boat. Then, they are forced to try to bear away while down speed, which is very difficult.

If you watch the video, Billy Besson shows the way to do it. Skipper and crew on the deck, both hulls in, jib well eased, delay the hoist until you get the bows down. Maybe that is why he is the defending world champ and currently winning the event.