I have a 965, had similar issues with a different HRM. I would, select “indoor cycling as an activity” on your watch. Pretty sure Zwift will see your heartrate.
When you are done, just bin your activity on your watch. Kind of a pain in the butt, but I’m guessing it will fix your problem. @Robby_Van_Mieghem
That’s not the cause. I have tried disabling BT on iphone.
Something has changed zwift or garmin
enrolled my self now as a beta tester on the forerunner, let’s see if that solves its fast