Fenix 3 REBOOT when starting a training session

Even with the latest firmware versions for the Fenix 3 (V6.80 and V6.85beta) we have seen at least on 3 different devices that our applications lead to a REBOOT of the watch if a session is started (FIT logging starts) and a heavy load via bluetooth happens from a mobile phone e.g. for changing configurations.

When disabling bluetooth on the mobile phone, everything is fine.

The mentioned applications are:
Running App Professional: https://apps.garmin.com/de-AT/apps/2e096d91-3e49-492f-9bd1-e5c92a53d1a5
Cycling App Professional: https://apps.garmin.com/de-AT/apps/9cbef7c8-9a7e-4f90-b4ef-42b11a11d8cd
Skiing App Professional: https://apps.garmin.com/de-AT/apps/47e87496-459b-46a0-8b9d-c344cb0d1df9

Sequence to reproduce the problem:
1. Establish a bluetooth connection via mobile phone to your Fenix 3
2. Start one of the applications
3. Start session by pressing the <START> button
4. Reconfigure configuration settings via mobile phone

Any hint to solve that problem would be great.