Sounds like either something on the boat or near the boat that is overpowering the GPS. Ensure that it is mounted outside of the radar beam, at least 6 ft from any AIS or VHF transmitting whip, and keep it away from any wifi or cell boosters. I have seen strong cell boosters on nearby boats cause problems for GPS. If the GPS is in the beam of the radar beam or near other strong RF, it will end up damaging the reception amp where it will become intermittent and eventually stop working. You should also ensure the GPS antenna is always used and stored in the upright position. I have seen many lose units by lowered masts where water condensates inside the srinkwrap and runs down onto the cable and up into the lowered GPS antenna. Hopefully this was an isolated issue.
