Thrust Lost in PosHold

Today, during a regular test flight got a sudden thrust loss and soft’ish crash… Analyzing logs and cannot understand what is going wrong. I found a quite strange behavior of the motor (actually I heard in field right before a crash).

Unfortunately cannot find what leads to that crash(well lost of thrust is rather consequence, right?).

The drone is about 1.2kg on 10" props plus 810kv motors, powered with 4000mah 65c battery. Its usual flying current is around 10-15Amps. From daily testing voltage around 14V (lowest on a graph) is OK and was tested before - it is completely flyable one. Vibrations seems to be quite low as well.

Please help me and point me out what parameters i can check?
2021-05-15 19-08-14.log.param (17.3 KB)
Dataflash log:

I’m using dshot protocol so that motors are connected to AUX1-4 -> C9-C12

hi, for me this is strange, you have to keep your THR more than 1500 to keep the altitude (1700 i think), so I think your drone is overweight… .then you were out of juice and your battery could keep the altitude…

or may be you lost a motor, the 9 motor…

Strange… value about 1700 most probably is a middle because the stick position was on a middle, so probably it is stick range/value calibration aspect.

The other point is that I saw that strange Motor9, and that is the question why control signal is so high?

Nothing strange about that. When a Motor loses thrust the command signal is increased.