Rocket into the sky

During my last flight I had an issue with pretty much hardware stable (as I thought) quad. I’m flying in AUTO mode. Right after takeoff quad started to climb at full throttle straight up into the sky. I tried to change mode to RTL with transmitter, but it had no effect and quad dissapeared into the clouds. After 20 minutes battery died and quad crashed nearby.

There is a tricky part. I’m using RTK GPS and trying to make a quad capable of precise landing, so during expirements I changed some of EKF parameters:

EK2_ALT_SOURCE 2 (default 0)
EK2_VELNE_M_NSE 0.05 (default 0.5)
EK2_VELD_M_NSE 0.05 (default 0.7)
EK2_POSNE_M_NSE 0.1 (default 1)

A few flights ago I switched to EKF3 as well.

After looking into the logs it turns out that EKF origin of quad was 2000 meters underground. GPS and baro were OK, but the error kept for 5 minutes, then altitudes suddenly came in sync.

Dataflash logs is here. Can someone help me determine the cause of that strange behavior?

Thank you for the help in advance.

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You had no prearm logging, so it’s hard to say, but when setting primary alt_source to something as sketchy as GPS, (even with RTK) you really need to check your instruments before takeoff.
Given the solid HDOP and fix reported, it must be some kind of bug in the GNSS processing code/chipset)

Also, you could have landed safely at any time by switching to Stabilize, ACRO, or any of the altitude-stabilized modes.

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It’s also not a good idea to have

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Just a guess here, but isn’t CTUN.Alt your baro altitude? If so, the copter thought is was -2000 below sea level when it started up?

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Did you set the rtl alttitude?it comes 20 meters default rtl alttitude.which flight controller are you using?after switching on th rtl switch did you turn it back off?it happened to me also and it almost reached the clouds and i was not knowing that it was going up 20 meters because of rtl and that time default rtl alttitude was 20 meters but after then i disarmed the motors and when it started to fall down and have reached very low alttitude i agian started the motors and safely please check the rtl attitude and lowest thurst to motors.I hope this would help you.Thank you.