Hi @RA_26,
Yep. Same problem. My Garmin Dual HRM stopped working after the update at the end of October. It pairs and then shows “no signal” when I use the companion app. If I don’t use the companion app then it pairs and the signal is received just fine. This means that I can have my Kickr Snap with either cadence or HRM. As a workaround I have been monitoring my HR on my Garmin Edge.
Just over the weekend I ordered a 4iiii Viiiiva HRM in the hope that it will combine HR and cadence on one of the two BT signals and then I have the trainer on the other. It just now dawns on me to wonder whether that means that I won’t be able to use the companion app anymore for ride ons and photos and stuff. Sigh. I guess I’ll see.
And here’s a link to a long thread about the “no signal” issue if you are interested: https://forums.zwift.com/t/garmin-hrm-no-signal-solved/209400/70
Good luck!