Need advice to improve loiter quality


I made a big sized drone and I have a question about Loiter quality.

It is composed of 100Kv motor, 30inch prop., octa coniguration and with 12S battery.

Tuning finished with no problem.

After taking off, when I go straight in Loiter mode, the drone moves to the left, and when hovering, there is a very minute toilet bowling symptom.

However, once the rudder turn (360 degrees) is in place, all abnormal symptoms disappear. (It really disappears every trouble.)

(But, it is happend again until the next flight until the rudder turn is performed.
It seems that doing the rudder turn will learn something (about compass?), but it does not seem to be maintained)

What other things should I check?
(The log can be attached only tomorrow, as it is on a business trip.)

Thank you

Recalibrate your compass, and make sure it is aligned with the frame correctly. And update firmware to 4.x.