My Apple Watch is not reading heart rate during workouts via Heart Rate app

When in a Workout, I often have many minutes where my heart rate measure is not working. It will say "Measuring..." in the Heart Rate app or a grayed out number with the "processing" heart in the Workout app. This typically happens until I open the Heart Rate app and watch it for at least a minute. Occasionally, I will get a suggestion to reset the heart rate (heart icon with a circular arrow in the middle).

What I don't understand is why the watch doesn't tell me it's having an issue reading my heart rate during a workout. If I step off my treadmill for a minute it repeatedly asks me if I'm done with my workout, but if my heart rate can't be read, I don't get a single notification??

I have some theories:

1. The watch isn't sitting on my wrist correctly so it can't read my heart rate. Understandable... by why no notification after a minute or two?
2. The watch isn't near my iPhone (and I don't have the watch with cellular service). This one shouldn't matter, and it may be correlation not causation. When this issue often occurs, I am walking with my husband and dog without my iPhone.

[Re-Titled by Moderator]

Original Title: Measuring Heart Rate for 2+ minutes without reading it