Help in analysis of logs after crashing(autotuning)

Hi guys,we were working on arducopter 4.0.5 quadcopter in X configuration ,20 kg ,actually a hybrid one (battery n engine).we have succeeded on our first flight test(but with heavy vibrations mainly in z directions and roll pitch and yaw delays ).After which we reviewed the logs and found these vibration issues ,On Auto analysing we have found motor imbalance just an warning.We have fine tuned and gone for the second flight.But the second flight just showed a more severe vibration on its first takeoff ,but later in the second one it was much more stabilized.We initialized settings for autotuning and then put the drone in autotuning mode .All went fine at the beginning the auto twitching was done by flight a few times ,but it went away sometimes when the pilot brought back the drone.And then one motor went off and the drone took a 180 degree flip and fell down.Please help in finding the reason for crash and also help us to fix the errors.sharing the link for logs below.

The reason for crash is exactly what you said. One motor (motor 2) went off. Either electrical failure (ESC, Cabling) or desync.
Also it seems that motors does not aligned well, since motor 3 and 4 works much harder than the other two, which means either the frame is flexed, or some motors tilted, causing a yaw which is counteracted by motor3 and 4.

Thanks for the reply sir,on further analysis we found motor 3 showing a high hizzing sound when compared to the other motors ,we found this to be a manufacturer error.sir if any other faults you have seen in the log analysis please mention that sir.