Problem with roll in RTL mode

I have aprduplane 3.4 on APM pro.
After installation and autotune the plane flies well in FBWA and auto, after this I installed the airspeed sensor, in the calibration flight I started in FBWA I switched to RTL, the plane loitered in a nice circle of about 145m radius. But the roll was not normal, the wind was 20km/h, when the plane is not facing the wind the banking was toward the center which is normal +17deg, but in the part of the circle where it is facing the wind it banks outside -10deg (the roll is negative), I have kff_rddrmix set to 0.5, I think that in this part it turns using the rudder.
I expected that the roll stays positive (to the right for clockwise loitering) and I can’t find where is the problem.

There is nothing wrong here. Don’t argue with success. Your plane was doing what it had to do to fly a circular path over the ground in a wind was 40 % of the planes airspeed, and it did very well. When the wind is at your tail the plane is moving fast and must bank harder to fly in a circle. With the wind on your nose the ground speed is low and less bank is needed.
It’s just physics. The slight negative roll was during the low ground speed portion and the wind was pushing it to the side and it was just doing what it had to do to fly the circle. BTW I estimate your air speed at 19.5 m/s ( 70 km/hr) and the wind at 7.5 m/s (27 km/hr).

Thank you for the explanation.