Heart rate undetected

This is an intermittent issue for me as well. I believe there is a lot of bluetooth communication between the AWatch and the iPhone when you start a Workout that prevents the heat rate to be properly tracked.

Normally this issue is only seen when recording a Workout. I believe after a reset it may start working but it is still an intermittent issue to begin with. But I think I have narrowed this issue down to the fact I started the Workout while wearing a bluetooth headset while listening to music or a podcast. It appears to be much more reliable if I start the Workout first then connect my bluetooth AirPods to start playing audio after it registers the heart rate.

Reset your watch by pressing in the crown and side button until you see the apple logo, then release both.