Tacx Flux connection lost when using Garmin Fenix 6 broadcast HR in Tacx app

I use the Tacx Training app on my android phone to connect to my Tacx Flux using bluetooth. No problems there.

However, when I start Broadcast HR in my Garmin Fenix 6 Pro watch, and also couple that in the Tacx app connection to the Flux is lost after 1 to 2 minutes in every ride I start.

I've tried the app on 2 different phones, but both give the same problem. 

As far as I can remember, this problem was not there when I started using my Fenix half a year ago.

Of course, I can start an Indoor  workout on my Fenix together with a ride in the Tacx app to save HR info, but then I will have 2 separate rides instead of 1.