According to the intensity minutes, my 4 week average is higher than what the fitness age is telling me. The fitness age is saying I need to increase both minutes & days, but the intensity minutes section shows I should have what I need. Is this happening to anyone else? It’s been weeks now!
I have the same situation just like you. 
I had to have couple of weeks break and just started with seroius training again, that's why I have only so much intensity minutes at this moment.
But the thing is that even if I have much more intensity minutes, it won't counted to the my fitness age 6 weeks average.
I never achieve the 3 days/week with high intensity even if I can see under intensity minutes section that I had even every day high intensity minutes.
The same for the intensity minutes average for one week in the last six weeks. I can see the at least 75 intensity minutes in the intensity minutes section. But it won't counted to my fitness age.
It is disturbing and disappointing 
If you can figure out anything else, please let me know.
Have fun by collecting your intensity minutes 
Update:
I went through all the relevant Garmin documentation 
and found out that it is necessary to connect my chest strap directly with the Garmin Connect App, even it is connected to my Garmin Edge.
Fortunately, older data were still saved on the chest strap( Pro), so my data have been updated in the app and I get know all of my intensity minutes under Fitness Age.
Hint: it does not work with Dual, because it cannot save your data.
I hope it will help you too.
