Apple Watch not recording workouts

Hello,

I bought my mom an AW Series 5. She noticed that when she is doing workouts mostly just speedwalking in her Activity app it'll show for example a 45 min outdoor walk but she'll only get 3 or 4 min credit in her Exercise ring. I told her that she was not walking with Enough intensity so I did an experiment and I wore my Apple Watch On one hand and wore her watch on the other hand and went for a 40 min run. My Apple Watch correctly showed 40 minutes of exercise and hers only showed 3 minutes!! I've tried to format and reset her watch but That doesn't fix the issue. Any ideas?