Magnetometer won't calibrate

Hello all!
I'm just starting to fly my RV7A. I have 2 G3X panels, G5 standby. The GMU 11 is in the right wing. CAN bus shows all green. GPS signal is good. I have taxied the airplane around the local compass rose. I have pulled the airplane around the compass rose with the tow bar. The system has even said "calibration complete".
I still can't get a good heading, off by 60 degrees and attitude is also unreliable. Taxing back from the compass rose this afternoon the heading actually showed the correct taxiway direction and attitude was good. I was ecstatic! Didn't hold, started drifting off. Any ideas greatly appreciated!
Thanks!
SteveL

Is in the wingtip? If so is it the end of the CAN bus? If so, is it properly terminated? Any chance the screws around it are magnetized?

Have you looked at the calibration page while you swing the ailerons? Mine was mounted too far aft on the wing rib and the aileron counterweight was too close and caused issues. Moving it forward one lightning hole made it work great.