Having the same problem here, even garmin express isn't showing data anymore. I have more than 70% free space on my fenix 3 hr. The android garmin app doesn't sync activities at all. Only if I pair my watch again it'll work for 1-2 syncs and then fails again. I also red that it might be a space issue but why doesn't it give a notification to backup your data on a cloud or locally and simply erase everything and start over, loading data from the cloud and newly stored data on your device? this goes on for almost 3-4 months now and I couldn't find a good fix to it. I don't want to wipe all my data. I want to at least back it up and load it from another source to see all the history since I'veb wearing the watch. This space issue should be done automatically, on a scheduled basis (eg during charging), if this is the case. I was really happy with the way this gadget worked. But now I have to waste my time in troubleshooting it. Pitty.
Can't sync courses to my Edge 810. The device appears in the list, but I can't select it (green checkbox) to push courses to it.
Also, the app never gets recent activities back from the website, even if these activities, recorded by the Edge and then uploaded, obviously passed through the app.