I've got a Forerunner 245 for a couple of weeks (got it second hand). I've factory reset it, paired it to Garmin Connect, synced and it worked fine for three days. Sometime around the fourth day it synced fine, but the heart rate data stopped around noon, it did not register steps, sleep, etc. The connect app day screen shows realtime data, but the history isn't updated. I've waited a couple of hours, and many syncs later data was still not being transferred.
I've done all the steps in "Troubleshooting guide for (some) data missing after syncing", but it did not fix it. If I remove and re-pair the watch it resumes transferring data on sync, but eventually stops. The first three re-pairs worked for more or less 24h, but after the fourth day it would work only for a couple of hours. I've really tried all the steps, and yesterday I've factory reset the watch again, removed and reset Garmin Connect Android and Web. It worked for 12h then stopped.
Another info. When a sync is correct, it shows on Connect Web the time of last sync. When the sync doesn't update data, it does not show in Connect Web at all. It seems like the problem is with Connect Android App not communicating correctly with the cloud...
So, I'm here seeking your wisdom. Anything I've missed?