I took off the copter using Stabilize mode, switched to AltHold mode and it all works fine.
Then I flip Ch8 switch to AUTOTUNE.
In a split second, all the motors seem to lose power and the copter fell from the air.

Can anyone help to have a look at the log and parameters file to see what happened?
Log and param file:

The crash caused the power cable to disconnect so the data after the crash is not in the log.

Thank you in advance!!

your front right motor failed to provide thrust (motor/ESC/propeller) , so it tilted in that direction, as a response you can see RCOU.C1 being commanded to a high level , and the opposite motor (2) go to idle.

you were flying at about 50% of the available throttle level, so with the effective loss of two motors, it surely looked as if it just dropped down.