Intensity minutes for Rowing

Intensity Minutes are calculated by the watch (if you own one). By default, it uses the internal HR sensor, so the HR may differ from what the strap records. In order to use the same HR data, you have to pair the strap with the watch, and start recording an activity on it (otherwise the strap is not used). At the end you can discard the activity. Or, if you own the HRM-Pro chest strap, then oppositely, you have to remove the watch from the wrist, and let HRM-Pro processing the Intensity Minutes. No other strap (except the new HRM-Fit) can do it, though

Yea that’s a little much. Sounds like a bit of a flaw in my opinion 

Not a flaw, it is expected to work exactly in this way. You can read more about it here: How Are Intensity Minutes Earned? | Garmin Customer Support 

I have the same question, except that I am finding that my intensity minutes are recorded for some Concept2 synced rows and not others. I wear a Forerunner 955 Solar, but don't record the activity on my watch but instead sync the rows from my Concept2 account. I'm finding that some activities show my intensity minutes (quite accurately) but for others no intensity minutes are shown. I haven't spotted a trend as to what may be the cause, but will keep investigating.

Actually I think the issue for me is that the intensity minute calculation does not always show soon after the completion of a C2 activity. Looking back at my activities, intensity minutes appear for most rows greater than 25 mins where I hit at least HR zone 3. But it appears the value does not appear until several hours after the activity. I assume this is calculated periodically perhaps.

No, it is calculated in real-time on the watch, and has no relation to any activities. IM are recorded round the clock based on the HR relative to the 7 days avg Resting HR (unless the option HRZ zones is available and enabled), regardless whether you record any activity or not. Please read the article linked in my second reply, to learn how exactly the feature of Intensity Minutes work, and what settings are available on your specific model. It is explained there in details.

I read the article. It explains the details but it doesn't correlate with my experience.

I did a 40 minute high intensity row yesterday morning and looked at the activity on the app about 30 minutes afterwards. No intensity minutes shown on the activity or added to my IM weekly total.

Seven hours later I checked again and now the IM appeared on the activity and my weekly total was updated.

IM's can be followed in real-time both on the watch, as well as on the app (assuming the connection between the watch and the phone works). I do it all the time - for example when riding an indoor bike, I can see the IM counter of the GC app incrementing every minute. If you don't, then either your HR is not elevated enough, or the connection between the watch and the phone does not work, but in the later case you would still see the IM's incrementing directly on the watch anyway.

I think you need to get past how it’s supposed to work. We understand how it’s supposed to work. 

what we are saying is that it’s not working the way it’s supposed to work…

im glad it works perfectly for you. Please understand that it’s not working for us.