Happy to see you made some progress, but you could probably get the external one working if you mount it at least 5cm (ideally over 15cm) away from any other device as the compass is extremely sensitive.
Another thing to check is also the compass orientation:
Checking Compass Orientation
- Ensure your AHRS_ORIENT parameter is correct. This will ensure that your internal compass’ orientation will be correct
- When rotating your aircraft through all axes each of the compasses should move in the same direction, and should be of approximately the same values
- Northern Hemisphere: - Z-component should be positive - when pitching the vehicle down, the X component should increase in value - when rolling the vehicle right, the Y component should increase in value
- Southern Hemisphere: - Z-component should be negative - when pitching the vehicle down, the X component should decrease in value - when rolling the vehicle right, the Y component should decrease in value