post 6 of the following link is a crash analysis by tridge that may look like to yours
Nevertheless, pitch and roll attitude estimation are very good and we can only notice yaw discrepancy from 480s.
Your Airspeed disagree strongly with GPS speed but you have airspeed disable.
I tried some time ago to fly auto without airspeed and I found that trim_throttle and trim_arspd_cm must be carefully tuned and matched. You have trim_throttle=20 which is probably too low to fly at 20m/s. If you look at ctun_throut you will see trim_throttle should be around 50.
So, you crash could be a stall or a compass problem or both.
I think the first yaw input is accelerometer sensor, compass and GPS heading are used to corrected accelerometer drift.