Garmin Connect appears to be duplicating Intensity Minutes with Vivoactive 3 Music ( VA3M) and Edge 1000, which pairs to another HR tracker.
For example, this morning I recorded a 25 minute cycle ride on the Edge connected to another HR monitor. I was wearing VA3M too. After the activity was saved, Connect claimed I had 50ish minutes of Intensity Minutes as a result, but should have been around 20 - 30 minutes. I started the morning with 0.
This occurs with every activity recorded on the Edge 1000 while wearing the watch, so Connect seems to be including Heart Rate on the VA3M, instead of discarding that HR data due to an activity in the same period.
The Activity with HR data should take precedence over whatever VA3M recorded and should definitely not be including both sets of HR data while calculating Intensity Minutes.
This did not occur with my Vivoactive HR.