I have not had this specific failure with my Raymarine system however I have had my share of issues. Most have been related to wiring or connectors. If you have any splices, check them carefully. I had an intermittent AP. Turned out to be an open CANL (white) wire in my stng splice. I could load software updates, etc. but the damn AP would occasionally go bonkers after making it all the way to Hawaii with no issues. It was a really frustrating problem.
Make sure the plug in connectors are making good contact. Unfortunately, in your case, that will mean verifying the wind vane screw in connector is clean and making full contact. Have fun up the mast. Raymarine will also tell you to make sure you are running the latest software on all instruments attached to the stng network. Nothing more annoying than to send a unit back to Raymarine only to have them tell you there is no fault.
BTW, during one of the SHTP seminars, Michael Jefferson talked about using dialectric grease to protect RF connections. After seeing corrosion in my wind vane connector when I had my mast out, I decided to apply dielectric grease to this connector in an attempt to protect it. I think this might be worth considering if you go up there.