Heart rate periodically vanishes from PM5 display

[Sakly]

The question is: what information is given by an average HR of an interval? I think for intervals averaging makes no sense as I need to know how much effort it took to complete the interval and that is given by the heart rate at the end, not by the average as this is highly depending on the rest period. The lower the heart rate is at the end of an interval of the same session, the better your fitness.

For steady state sessions it does not really matter, as your HR will not going from lows to highs so much and if you need more exact data from PM5 increase the number of splits in your session to get more data points. In fact any connected app will calculate that for you, so usually no need to do so. If only using PM5 this can be a solution.
For my steadies PM5 and ErgData average typically differs by 1 or 2 beats.