I had a very similar experience this past weekend. I drove Houston to Austin for a race bike loaded on a hitch mounted Kuat platform rack. Everything was working fine when I left, but when I arrived in Austin, and went out for a warm-up ride, at first the quarq would not sync to the 310XT at all, then I got some intermittent data. Race morning I replaced the battery just to be safe, and the unit paired, I also ran qalvin diagnostics and everything was fine although zero offset moved a great deal. When I went to start the bike leg.. nothing. Then throughout the 2.5 hr ride, it was intermittent at best. I returned to home and have had the same experience. Syncing to Qalvin resulted in no Cinqo found, then take battery out and replace and it will sync.