ORIGINAL: kimhey
That sudden/abrupt nose down change from straight and level flight at what seems like way over stall speed, outrules stall in my opinion. if only one flap did lower, I believe the airplane would start a roll only, not pitch down so violently.
To me, it looks more like a total signal loss. Have you tested the RX batteries under load? The forces on the flaps can be quite substansial.
The plane had rolled to the right and was inverted. Then it apears a pull up on the elevator caused the dive.