Had an interesting event happen the other day. While flying in auto on a mapping mission, the copter (an s900, pixhawk, AC3.2.1) did some unanticipated roll movements during a turn at a way point. It proceeded straight along the flight plan as planned, and then started wobbling again (20 deg of roll or so). I switched to loiter and the copter stabilized level, BUT proceeded to descend (quite rapidly) until it hit the ground. While it was coming down, I pushed the throttle full up, but nothing happened. If I had the presence of mind, I would have tried manual, but didn't get to it. Broke a few parts, but the damage wasn't bad. I've reviewed the log a bunch, but can' t nail what caused the issue.
The auto analysis points to problems with the mag field, but I received no warnings.