So most of the problem with the Garmin G-Wind is they did not properly terminate the RS485 bus at the GND-10. The underlying up/down mast is the old school Nexus network, from when the instruments were made by Silva.
Anyhow, the fix is pretty simple. Add a 120ohm resistor across the data pair down at the gnd-10 end (or close by) and the unit becomes extremely reliable.
We actually figured this one out trying to troubleshoot things, and noticed that it was stable/reliable when we had our old Nexus Wind head unit connected to the nexus side, and unstable with it disconnected. Put two and two together (I'm a computer Engineer old enough to remember termination resistors) and boom. Done. It's now worked reliably for 2 years, except for a brief period when the up-mast connector got filled with bird crap.