I have a new vivoactive 4s, and also have a Gramin Edge 830. One of the main things I wanted to do with the new 4s was broadcast my wrist based HR to my Edge 830 while cycling. While the wrist based HR seems very accurate when I record the activity on the 4S (running, HIIT, etc), it's extremely low when using the broadcast mode and broadcasting to my Edge 830. Here are two cycling activities where the HR is extremely low (I even noticed looking at my watch, and in the toughest parts it was just stuck around 80-85 bpm):
connect.garmin.com/.../4126821502
connect.garmin.com/.../4105199823
You can see in the second one, I had to stop and restart, and it seemed to work for a little while. However, in all scenarios, after a little bit of time, it gets stuck on 80-85bpm.
Here is an example of accurate HR from the watch when I run and just record the activity there:
connect.garmin.com/.../4123829857
I've read similar issues on the forum for Fenix 6 users, so hoping this is a bug and FW will fix it. Otherwise, I will need to replace the watch.
I'm running FW 3.40 on the Vivoactive 4s and 4.10 on my Edge 830. However, as I've stated, I can actually see on the watch when it glitches up and won't go above ~85bpm.