Beta Blockers and Exercise Tracking

I take a Beta Blocker medication to lower my heart rate. Consequently, even with brisk walking, my heart rate only reaches the mid 80's. My Apple Watch isn't picking it up as exercise. Resting heart rate is in the low 50's. I am pushing a stroller with a 35lb passenger, and walking briskly.

I'm very disappointed because the main reason I got the watch was for the activity tracking.

I can't be the only one who has this issue?

Is there something I can do to remedy this or is it on Apple's end?