You probably have already refreshed the firmware on the RC and AC
Done the RC calibration following the blue dot
DJI Assistant 2 has the reset to factory settings as well
So it flies perfectly straight on forward and backward stick but when you release the stick completely (no fingers on it) it banks to the left as it slows down and then hovers in a new spot 2 meters to the left?
Does it do this from any speed e.g full throttle forward or when it's slowly flying forward ?
Are you using a mode 2 stick configuration ?