Intensity minutes not working - what is going wrong with this device?

Intensity minutes are playing up on my Fenix 6 too. Used to be okay but now doesn’t measure consistently or reliably. I’m surprised how this issue is talked about so much and over a long time and Garmin just seem to ignore it! I guess that either means they don’t have a solution or they don’t care (or both!) 

Too true.  I won’t buy Garmin again.

Intensity minutes and vigorous minutes stopped showing up in my trainings after I've started using Edge 830 with HR strap and this worked normally on Venu 2 with optical HR.

I can't speak specifically about the Edge 830 but my Edge 130 Plus isn't a tracker. In order to get the intensity minutes, I continue to wear my VA3 while using my Edge. However, I don't start an activity on the VA3.

My Forerunner 245 didn’t register HR reliably for a long time. Then, one day, it suddenly started working. Months later, it lapsed again, stayed that way for a few weeks, then started working again and has been reliable ever since. I suspect there were software updates taking place, some actually broke what had been working, and there was a break-fix thing going on, but finally one came down the pipe which provided a lasting fix.”Intensity minutes” were the same way.  Programmer turnover @ Garmin must be pretty regular…

I have not changed any settings, when I do my "power walk" flames show on my watch. When I end and save the walk then my phone app picks it, there are zero intensity minutes. Clearly, something's gone amiss.

Correct me if I am wrong, but you have to be sure that you have at least 20 minutes in a row at a certain HR.  That being said, you all are right.  I love the idea of the intensity feature.  It is one of the best features offered in my opinion.  The problem is that it has never worked reliably over the +10 years that I have owned Garmin watches.  I’m still a loyal Garmin guy (Edge 840, Rally Power Meter, HR monitor, Varia Radar,  Varia Headlight, and Venu, but have given up on this feature.

The same on a Venu SQ2 

Settings:

• Pulszone for IM: Enabled 
• Zone 3 for moderate and Z 4 for vigorous
• No 10 minutes requirements to register IM on this model

At today's activity I was in zone 3 and 4 for more than 15 minutes according to the watch.

But it only registered a total of 6 IM. 

I see a lot of posts on this issue, but no solutions.

Has anyone got help from support? Or any solution? Restart? Factory reset?

My intensity minutes only calculate when I have my Garmin watch on. But when I cycle using my Edge 830 along with my heart rate monitor and no watch... it doen't calculate anything.