F5 Sync problems

Hi,

I have my Fenix ??5 for about 1 week. Since yesterday, it can be coupled with the smartphone (Honor 7) and I receive notifications from the phone on the clock, but the synchronization process always stops after about 5 minutes without syncing HR data or similar. Synchronizing with the USB cable via Garmin Express works fine. I have already deleted the Android app, removed the watch on the Android app and in the browser, reconnected it first via the Bluetooth menu and then via the Garmin Connect app and restarted both devices and checked for system updates. Unfortunately, nothing helped.

Is there anything else I can try, or do I have to send the device back?