Crash after autotune


Yesterday I went to have a maiden flight with my newly built quadcopter. It’s using a pixhawk cube, on the latest arducopter firmware.
The flight was stable, went to fly few circles without a problem, than I set up the autotune.
After tuning one axis, I got the notification on the ground station, autone is done, and in the same moment, the drone started to descent aggressively.
What I saw in the log file, is a radio failsage, but everything is hard wired, receiver has its own 5A bec, and it has a telemetry. Ground station didn’t warn me about a telemetry or signal loss, so I think the power is fine.
After the crash, I checked everything, and did a second axis tune, where the exact same thing happened, atutune done, and the same moment it crashes.
Can somebody check the log, and suggest something?
Thank you!

It seems the radio failsafe was the initiator.
The descent initiated at that point.
Your GPS values were very close to minimum requirements and I think the EKF might have had a hand is refusing your auto selection but might have been inadequate for the RTL function.
You seem to have a radio reception issue to deal with first.
The autotune seemed to be going fine up until that point.
I would have a careful look at your RTL and FS parameter settings.

Thank you very much.
Few more things:

The drone was flying without a problem, no radio errors, no failsafe before the autotune.

The drone started to fall, when the ground station announced “autotune done”.

And the exact same thing happened twice.

Pitch autotune - ground station announces the finish - crash

I checked everything, and again

Roll autotune - ground station announces the finish - crash

And the failsafe value is 975, and if I’m correct, based on the log the lowest on the throttle was 1000.

Could it be a bug in the firmware, or what I think more likely, radio error?

I’m using an all-in-one radio, android tablet built in the remote, and it’s using one radio for control, telemetry and video.