Why my regular activity was not counted in intensity minutes?
Possibly the heart rate was not sufficiently elevated, or your 7 days avg Resting HR is too high. Verify whether the HR during the activity was at least some 150% of the 7 days avg Resting HR. And if you have an older device, then there is an additional condition, that the HR must be continuously elevated above that level for minimally 10 consecutive minutes, in order that the Intensity Minutes start to be counted.
Another possibility is that you did not use any device supporting Intensity Minutes (some old watches do not have that feature, and also most Edge computers do not support IM), or that the Intensity Minutes did not sync to Garmin Connect - for example because of a file corruption due to a crash and reboot of the app during or after the activity. Not having any line on the IM graph during the run indicates that it could be the case. Try syncing the watch over the USB cable with Garmin Express, to see whether it can load any missing data.
Didn’t have any issue until today. Why my regular activity was not counted in intensity minutes?