I seem to have missed a key point in the log here - There is a big mismatch between the 2 compasses Z values.
The external compass (compass 1) gets a constant error after the engines start.
(See Mag.MagZ vs Mag2.MagZ vs ThrOut)
I don’t think it’s a Compass-Motor mag field problem because the log shows a (big) constant error and not a disturbance
The compass in this build is not elevated above the quad (on the same plane as the motors, in the middle of the quad. The quad is 550mm diagonal), however I don’t remember ever having this problem.
Yes - It was a compass-motor interference after all. Recalibrating the CompassMot parameters fixed it.
To be on the safe side, I’ve moved the compass to a pole (elevated from the motors plane) so it’s farther away from the motors.