Copter suddenly falls, Roll and Pitch diverged from DesRoll and DesPitch

ArduCopter Copter 4.0
1

As the tittle, I have my F500 frame with Cube Orange, Copter 4.0.3. When flying, it behaved like losing thrust at 1 motor and spun spirally, hitting the ground. Exploring the log, I saw the inconsistent between Roll and Pitch vs DesRoll and DesPitch.

2560×1395

This is the full log file
https://drive.google.com/drive/folders/1lZ5bRYwwJCHFTOw5QLwvTjrd91h3CTnE?usp=sharing

May I have your ideas.
Thanks!

2

Looks like thrust loss on Motor 4. Motor, ESC or Prop failure.

3

Thanks, based on your observation, I dived more in the log and found that battery went low at that moment. I am concentrating on both the battery and mechanical stuff and get back if anything happens again.