I check my lowest measured heart rate in the morning. When I look at it again later in the day the lowest number sometimes has been upped by a few bpm. Sometimes it does that in steps during the day. When I do a workout my peaks can be lowered over time. And not just a little.
Like I see my watch while exercising telling me I'm in a hight range, well over150 bpm. Half an hour later my Garmin app shows me a peak of 135 bpm. And yet a few hours after that, it may lower that same peak to say 123 bpm.
Why do the recorded data change over time?
I can get it that it does not show all the live peaks that I see during exercise. That there is some topping off there. That makes sense. But don't get the changing of data afterwards. Sometimes the changes of the graphs happen after more than a day.