Quad sudden lost power and descended to ground

My 500 size quad during hovering suddenly lost power and descended to ground. I forgot to observe the LED on the FC. Attached are 2 BIN logs, one using 4 cell battery, and this flight experienced loss of power. The other BIN Log was for a 3-cell LiPo flight — there is no loss of power on this flight.
Could anyone offer some help to interpret what has gone wrong. This is the second time in 2 days that loss of power happened on 4 cell.

Thank you for your help.