Uncommanded change from manual to RTL

The skywalker X8 made an unsheduled arrival on it’s first flight when it apparently went into RTL without “permission to do so”. I cannot see any parameter that would have caused a fail safe condition. I am having trouble finding my way around the logs even after reading the wiki and need a bit of a hand. I’m using apm2.5 with external compass, a cheap power module which only supplies battery data and a nexternal voltage regulator to power the input side of the apm while the speedy powers the servos.
First flight was going OK and briefly tried FBWA mode before switching back to manual and then before I could land, it went to high throttle, banked right and headed down.
It’s ready to fly again and I have loaded the latest firmware but sure would like to know what happened before I go again.
Logs attached.

the .log does not contain anything that suggests RTL, but ends mid air, at about 30m.
also , your VCC voltage is no good, APM is fed from a very unstable source that delivers 6.4volts one moment, and drops to 5.2v - while 5v is enough, such bad ripple is no good.

Also 6.4 volts, depending on the equipment connected to APM, would overheat it’s linear 3v3 regulator.

The tlog shows an RTL just before the crash. I don’t know why it would show in the tlog and not in the .log.