[TG] [TG11] Smart Pilot X30 losing calibration

[Azura]

I have an SPX30 and an ST70 controller. Recently I started having a problem with the autopilot not maintaining course. It suddenly made a 30 degree course alteration, and the fluxgate compass was off by around 30 degrees. I ran the calibration procedures, after which the fluxgate agreed with the binnacle compasses as well as the gps. The system operated normally for the rest of the day. A few days when the ST70 booted up it indicated "calibration needed" and the fluxgate was again reading more than 30° off. This time I didnt have time to do the circles so I just synced it with the gps, and it worked for a while, and then started going out of calibration.

Yesterday I was looking at the compass calibration field and I found that there was already a -100° manual offset, which I assume was done the previous owner. I increased it to -130 to get it to match my binnacle compass which was reading 60°. After a few minutes the fluxgate compass started increasing and after a few minutes it was reading 68° even though the boat was tied to the dock. At some point as I was scrolling through settings that manual offset was lost, so suddenly the compass was reading 172° when the boat was pointing 60°.

I located the fluxgate compass to look for potential interference and found it had been installed right next to the batteries, at waterline, facing forward. (Is it acceptable to have it so close to the batteries? I believe it was factory installed there by Jeanneau.)
I tested the fluxgate with an ohm meter and it checked out as per the guide.

I am planning to make another attempt at calibration when I take the boat out this weekend, but I was hoping I could get some advice as to what else I should test or look for.

Any help would be greatly appreciated!

Ian