Having gone through almost every inch of Raymarine
cable on my boat and checked every sensor, readout, etc. I agree with Goboating, it's almost certainly the computer reboots that cause the loss of heading.
Spikes on the power line would seem to be the most likely cause. Check the power cable, all connections, all splices. Connect a ground. I don't know how yours is set up but maybe a ferrite on the power cables
?? Of course, ferrites probably aren't too common in the San Blas, and wrapping a mola around the cable won't cut it.
And, worst case, perhaps your computer has an intermittent problem. That's why I suggest contacting Raymarine
. Here's the closest link to their tech support. You'll have to set up an account with them.