I was having many problems with 3.1.11 MP release. So, rather stupidly, I updated to the latest beta. Most of my prior issues were gone, good.
I do a pre-launch calibration after the accels and barometer have warmed up. I took off (fixed wing) went to Auto and noticed the plane was in a constant roll of +12 degrees! I RTL'd. When I got home I tried to figure out what went wrong. After a couple hours, I quite accidentley found that doing the pre-flight calibration had set "level" for the plane. Well my plane was not level but that's where the IMU thought level was.
Beware if you use the pre-flight cal.