Welcome to Justanswer.com, my name is Dustin.I'm sorry to hear about the issue you are having, I will do my best to help you resolve it.
Many times this is a sign that your software firmware needs to be reset or refreshed. Your best bet here is to update the internal software, as that usually cures issues like this.
To do so, go to this page and download the update
Then, follow these steps to install the update.
Then, To be safe I would take your vessel out in clear weather and try navigating for a bit.. If it works afterwords without issues, then we know we have solved the issue.
Other wise, you may want to check all your cables, power cables, network cables, everything, for any corrosion at all in the connectors or any damage to the cables themselves. And if you find any corrosion or damage, replace the cables. If you need a reliable and low cost supplier to replace any specific cable, let me know.
If you have further questions, let me know.
I strive to provide great service, and greatly appreciate a 5 star rating clicked and submitted when you are satisfied.. I always answer follow up questions.Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.