Crash by reboot APM 2.5 ?!

First of all, Sorry for my english
i have a (big) problem with my APM, as i was in flight my X8 (3kg) fall like a stone from 20 meters height!

Here are logs of this crash : … 5.png.html … 6.png.html … 7.png.html … 8.png.html
After the crash, the APM sounds like it was rebooting and on my FPV sreen i saw the minimosd rebooting

It’s not the first time that has occured… I have allready lost control of my multicopter but it was at 30 cm height so i had no domages.
Nb: before this crash, i flown severals times without any problem

The APM is powered with a 3S connected to one external UBEC 5A 5V connected in one output port (every red wire from ESC have been removed) (i have a 4S for motors). Both batterie where fully charged

Thanks in advance for your help

Upload LOG

Yep, APM died in flight. VCC average is 4.74, min 4.67. Most likely, you need a higher input voltage.