Drifting Problem with the Mobula6

Hi

i recently got my Mobula6 2,4Ghz ELRS tiny whoop in the mail and was very excited to try it out.

The problem is: the longer the flight goes, the more heavly it starts drifting (in my case to the right).
Always the same, when i arm with a fresh battery leveling in angle mode looks awesome but the longer the drone is armed and flying the heavier the pull to the right gets. almost to the point where full stick (left) is not enough to compensate the drift.

I have already contacted happymodel support and they gave me this link:
https://oscarliang.com/drifting-problem-angle-horizon-mode-betaflight/

After applying the "fix" the drift is reduced but after 1:50 of flying the drift is very present (and annoying) again.
Leveling my acc after every battery reduces this but i am not able to get it completely right.

Do you guys experience this also?
Is there anything i can try besides sending it back to the seller and hoping that another one doesnt have this issue?

Thanks in advance for any help!