My Garmin Forerunner 45 recently updated itself to software version 5.10. The day after, I could sync activities, for example a walk, to Garmin Connect on my Android smartphone and this activity appeared when I looked on Garmin Connect web. Heart rate and steps updated in real time on Garmin Connect Mobile. When I tapped sync on the app, it tried for quite a while, maybe 30 secs, but the step data never made it to Garmin Connect web. I tried syncing via Garmin Express on my Windows PC and this failed to sync.
I tried "switching off and on again", both watch and phone. I un-paired Bluetooth and re-paired. I deleted the device from Garmin Connect mobile & Garmin Express and re-added. I did a watch reset without deleting all the data. None of these worked.
Eventually I did a complete watch reset deleting all of the watch data and removing it from Garmin Connect and Bluetooth, then re-added and re-paired as if it was a completely new purchased watch. This did the trick and it's been OK for about 24 hours now.
My wife has a Forerunner 45S and we discovered exactly the same symptoms on hers this morning. She uses Garmin Connect app on an iPhone SE. Her 45S did the same update and has ended up with exactly the same problem. We tried all of the same things as I did with no success. About an hour ago, we did a complete reset on her watch and it now seems to work OK.
As an ex-IT software specialist, I think it's pretty conclusive that the software update process caused these problems!
