Pixhawk flyaway in Alt Hold


After lots of flying with my 3DR DIY quadcopter, I decided to upgrade to a bigger multirotor on the 3rd flight. I was hovering in Alt Hold mode when suddenly the quadcopter started to gain altitude, none of the controls were working and neither was the RTL. It flew out of sight, crashed into a tree and fell to the ground.

I have been looking over the logs for 2 days now and have been through the Wiki. I can’t seem to see the issue.
Any help would be appreciated. I would like to find out what the issue was before I fly it again.

Tarrot 650 frame
Multistar Elite 3508-268KV
Afro 20 amp esc
X8R Receiver and Frsky Taranis Radio
Pixhawk with v3.2 firmware
APM Power module
6s 5000mah battery
15 inch Propellers

Like you said, nothing terribly obvious right off the bat. There are some radio failsafe and EKF errors at the end but I assume that was due to the crash. The flight mode is in RTL then switches to Alt Hold then back to RTL. Desired alt, alt, and baro alt all track pretty well. Could it have been trying to climb to the RTL altitude but flew the wrong direction due to compass interference? It did switch to land mode at the end there. If you can describe the behavior as you cycled through flight modes it may help me or someone else correlate what happened in the world to what the logs show.

Hi Matt_UAV-America thank you for the reply yes the failsafes at the end are from it hitting a tree and going out of range.

I was flying about 4 meters in front of me and about 3 meters high in stabilize mode I went into loiter for a few seconds and then into alt hold flew for a little while then she just started to climb with out any radio input at this point I know something was wrong as it was not responding to any radio input so I hit the RTL switch witch did not do anything so I took it out of RTL and then back in again but still nothing once she reached a fair altitude it took off in a bit of an arc to my left flying for a while randomly until it hit a tree and then crashed.

I had tested the RTL a few times in the previous flights and it worked perfectly with a RTL altitude of 3 meters

Thinking about it now I should have cycled through the flight modes to see if that helped.

I’m going to elevate this one. I can’t figure out what happened.