Apple watch exercise not matching recorded workout

I took a picture while fully recording a 45 minute walk, my exercise ring shows only 37 minutes of exercise completed. How can my fully recorded workout not line up with my ring? I've experienced this before but was able to snap a picture this time. I had walked 1 hour in the morning and 1 hr in the evening my ring only reflected 35 total workout minutes??? I read other threads about your heart rate not being high enough to count but how would it not count if actively recording the entire workouts??

For today after continuing to walk my ring is consistently 10 minutes behind my actual