Crash investigation: motor power loss?

I had a quadcopter that crashed with no warning today. Based on the log files, I suspect a motor power loss. All the motors are spinning after the recovery, and I find no indication of a damaged motor or bearing. The propellers were all damaged in the fall, but I don’t have any indications that a propeller was damaged before takeoff.

Takeoff weight: 3.0 kg
Propeller: T-motor 16" carbon fiber folding
Motor: T-motor AG4006
ESC: T-motor F55A

Flight log available here:

Does anybody here have a hypothesis of why my quad decided to crash in the forest?

This is unrelated, but please upgrade to at least ArduCopter 4.2.3

I would say motor3 then motor4. It could be something went wrong with the prop folding mechanism because severe vibrations start at the same time

Z axis vibrations were less than ideal before the incident, so that’s something to address in the rebuild.
Stability was only lost after the motors went bad.