You're probably referencing my post:
Horizon Tilt regardless of Gimbal Roll Adjustment mid flight
Why some birds experience it and others don't, I don't know. Could be quality control issues with the sensors, could be interference where you fly, could be the way you fly. Could be all three. I've found that (referencing my attached post) the way you fly seems to have a pretty big impact on whether or not the problem presents itself and how bad it is when it does. Until they address the issue with a fw update, you're basically stuck having to counteract the issue by doing the opposite of what caused it. Also, unless you have a truly screwed up gimbal where even after a calibration on a perfectly flat surface you need to manually adjust the roll before you've even left the ground to get a "true level" (in which case send that bird back to DJI, it ain't right), you should never have the manual roll adjustment set to anything but zero. It will only cause headaches you can't fix because when your horizon screws up again...and it WILL get screwed up again, now you are trying to correct a titled horizon back to +2 instead of back to 0 where it should have been in the first place.