After last update on Aug 18 Garmin Connedt stopped to synchronize data with iOS. Any ideas how to fix it ?
Do you see the Green circle around the image of your device and the circle completes as it attempts to sync? Any error messages? Make sure you're logged into the app with the same credentials as on Garmin Connect Web and Garmin Express.
Data is Missing from My Garmin Connect Account After Syncing | Garmin Support
That would indicate that the sync itself is working, which is why I suggested the possibility that you might have logged in with a different account than in the past. Happens frequently when logging out then logging in to the app after a version update. Might be worth at least checking the link I supplied above.
Also, see if you can sync manually using Garmin Connect Web. This would be a way of checking if you have any corrupt files on your Garmin - How Do I Manually Upload an Activity I Recorded to Garmin Connect?
My Garmin Connect iOS stopped updating Health Kit as well after the update to latest version on August 18th.
A Phone reboot solved it. But force closing Garmin Connect (swipe up) did NOT help the issue.
My phone is running 2nd public beta IOS 15.