I doubt it has anything to do with Seguin. Seguin would only be a minor local effect.

My Point-1 GPS/Compass or the Lowrance plotter seemed to act up part way through our passage from the UK to Holland, and I rebooted and otherwise struggled to find anything wrong. Then the next time we headed out it started working fine and continued to for the rest of the summer. Go figure.

I seem to recall I've seen a little compass wackiness years ago in the vicinity of Seguin but it's been awhile so I can't be sure.