Garmin Connect isn't properly syncing with my C2 logbook.

I do not know what a C2 logbook is, but if it is a Garmin device that syncs to the app over Bluetooth, then check out the tips in the Sync / Connection Troubleshooting Guide. 

I guess it's the app used to capture Concept2 rowing machine data. Concept2 Logbook

The C2 Logbook is a website much like Garmin Connect; however, it only tracks rowing data. From what I can tell, the only way to get my complete rowing data to Garmin Connect is to use a phone app called "ErgData" which only syncs to the C2 Logbook, and then the C2 Logbook is supposed to sync to Garmin Connect. It used to work just fine but doesn't anymore.

From the Garmin Connect website, if I click on Profile & Account ~ Account Settings ~ Account Information, it shows that the logbook is connected. But for some reason, it's just not syncing.

Try disconnecting and reconnecting. If it does nt help, try asking at C2 - they may have some kind of log, that could reveal why it does not sync, or they can already be aware of some recent incompatibility.

Thanks, trux. As I said in the OP, disconnecting and reconnecting seemed to work for a day, then it stopped syncing again.

I'll reach out to the C2 people.

I have a connection issue. I use a pm3, with a cable. My data will go from erg data app to the log book then sync to Strava but not into garmin. When I use a pm5 it works properly. 

Interestingly if I use the boat coach app in place of erg data app with my pm3 it does sync, though some data is corrupted.. 

All very odd