My 2 cents: I have a VP1 and after more playing than it should have taken, I noticed the magnet for the anemometer is in the cup assembly, and the reed switch is in the holder/base thing. This would mean if the cups dropped just a little too much the magnet would trip the reed switch every once and a while, generating strangely low readings. Pushing the cups up should solve this, but for a more permanent solution it seems you could push the magnet up and epoxy it closer to the reed switch.
I hope it yours keeps working!