I've calibrated the compass (using methods in various YT videos) several times. Each time I get different offsets for the calibration even though the machine hardware and location remains the same.
On every flight I get EKF warning of compass difference.
I have not done a compass MOT because I read somewhere that it shouldn't be done. But I can't find that text anywhere now.
What is the best method to get the compass calibrated correctly ?
Compass cal will vary by as much as +- 50 so I would not put to much stock in that.
For some reason the internal and external compass are deviating from each other possible causing your issue.
If you could provide a log of the issue that may help.