AC-3.3 X4 copter uncontrollable Yaw spin descent to ground

Hello all !

I’ve recently set up a new custom X4 frame with these specs :

I have an important issue with my setup I can’t find the reason… first time I’ve seen this happen.

In STAB mode, when I try to hover, my copter rapidly starts spinning CCW and loose altitude even if I try to correct with manual yaw / throttle input ! There are no Roll / Pitch deviation and the copter keeps its attitude right. Just a Yaw spin making him fall to the ground.

I checked the logs of multiple flights. I can’t fly more than 10-20 sec anyway so I did a lot of test flight at 1-3m height to prevent damages.

We can see that the AP is reducing motors 1 & 2 (CCW) while increasing motors 3 & 4 (CW) to correct the yaw spin… but it should do the opposite ? CW motors generate CCW torque ? am I wrong ?

Anyway, since copter prioritizes attitude over throttle input… motors 3&4 go to max and 1&2 decrease a lot so the average is below the hover position and copter falls slowly to the ground.

I’ve checked the motors layout and spinning direction, MAG/IMU/AHRS datas looks good, when i spin left/right pitch up/down , roll left/right, I can see it’s working as it should on the mission planner HUD.

ESC calibration was done and re-done.

I tried to check if it could be a battery power failure but Vcc and battery voltage don’t drop that much and I don’t know why it would always spin CCW…

CoG of the copter in a 3-4 cm behind the CoT. Autopilot is on top of the CoT.
Copter is symmetrical on the roll axis. Motors are not twisted more than the eye can see (1-3° max).

I uploaded 2 logs from two differents days… Hope you can find something I missed !
(Sometimes I let the copter on the ground with 20-40% throttle and gave so yaw/roll/pitch input so verify the system and to test the battery on 20+ sec flight as I suspected a power failure at first…)

1st day of flight :
2nd day of flight : (Big file sorry, I logged ALL data…) :

Thanks a lot !!

did you solve the Problem?
I think I might have the same.
Copter spinns very fast in yaw.