For pete's sake I walked fifty minutes this morning with the fitness app running.

Is anyone else having a problem with this. I have an apple watch 3. I am on my second one because apple told me to return the first because of the same thing. I averaged 135 BPM for 49 minutes of walking and got credit for 35 minutes of exercise. I had a 1 and a 2 previously and have never had this problem. I shouldn't have to work to physical exhaustion to get credit for this. at my age the target is 92 to 143 BPM to for exercise so what is the problem?