Unknown crash, need help debugging

First pixhawk quad. It’s had a few short small, low-alt flights. But this was a quick 50m high mission, and it suddenly free-falled from the air. Can anybody point me in the right direction to debug what happened? The log can be found here https://drive.google.com/file/d/1JQZR20A_B1TiR6p6U-zZkDhqQl2DN0GJ/view?usp=sharing

Even if you just direct me into what values to look at, I would be very grateful. Thank you.

Loss of thrust on Motor 2, Motor 1 dropped to compensate and down it goes.

Flying on default parameters? You should have set the Initial Tuning Parameters before 1st flight.