Quad took off by itself after arming and flew away

Very strange flight today. After completing a number of missions with 3 to 4 waypoints followed by picture perfect RTL landings - upon re-arming in Stabilize mode, the quad went to full throttle, leaped into the air and flew away. It flew over an office building and went out of sight. Somehow, it landed a couple hundred yards away in a parking lot with minimal damage. After it took off, none of my inputs into my Spektrum DX7 seemed to effect the flight. I perused the logs - I’m not an expert - but didn’t see anything extraordinary. I’d appreciate if someone could look at the logs. My biggest concern is why the quad would take off by itself immediately after arming. Logs attached. Thanks!!!

Quad: 3DR DIY Quad
Pixhawk running 3.15
Mission Planner 1.39
2216 800 KV with 11/4 props
3DR External GPS
5000ma 35C lipo
3DR Telemetry
Spektrum DX7 (using only Sat receiver)

The copter seemed to do exactly what is was told to do via the RC inputs.

The file Flyaway1 shows that throttle out followed throttle in, as well as the pitch and roll inputs.

Backing up in the control chain a little farther, the RCInputs file shows the logged RC inputs. It shows in particular channel 3, throttle, going max. Thus, at least all the commands were coming from your receiver. Whether the receiver did this on its own, or followed your inputs, that’s for you to say. The inputs were varied which looks like you were trying to fly it.

However, I’m also not an expert in logs!

I actually had this same problem! However, my logs show no throttle input from the controller. Please review my logs below - 3DR looked at them and couldn’t find why it took off after being armed but before throttle input.

I have a 3DR X8 and a Pixhawk, and am using Mission Planner.

Here is the dataflash log file from the Pixhawk.