I've seen reports of the watch reporting low heart rate, and my wife sees that occasionally on her Vivoactive 6. For example, on a hike she can have a heart rate in the 80s when she can tell it should be at least 110 or 120. After a while, it will jump up and be fairly accurate for the rest of the hike.
However, that's not as big of a concern because it doesn't affect her zones and other calculations. The concern is that it shows a maximum heart rate during a workout as high as 230 bpm and she is a 64 year old. Worse even, is it calculated a maximum heart rate for computing zones that is around 205 bpm, again a heart rate that is observably too high and unachievable at her age even though she is fit.
We bought the Vivoactive 6 because her Fitbit was not reading her heart rate properly and I wanted her to have a real fitness watch (I've been using Garmin for 20+ years).
We've rebooted it and made sure it was on the latest firmware. She is losing faith in the watch and I am thinking about replacing my Venu 3 with a Venu 4, but since they have similar firmwares, I am a bit nervous about it.
Any ideas what else we can try?