I have noticed this in the bike activity (maybe it happens with other activities as well).
After doing the activity for a while (more than an hour), the calories start to get understimated for the last laps.
For example in my first lap, warming up, it shows 10 cal per minute (at an avg HR of 120, with a max of 138). The last lap shows 139 calories in 25 minutes (that is less than 6 cal/minute), even if I was at higher HR (avg of 136, max of 148).
This happens all the times when I do workouts of more than 1h15 min
