Hello Jecasogo!
Thanks for reaching out to the Apple Support Communities. I understand that the workout on your Apple Watch is pausing, but it’s still tracking your heart rate. This issue just began 2 days ago. You’ve done a great job checking the fit of your Apple Watch and ensuring that it’s tight on your wrist. Next, begin by restarting your Apple Watch and your iPhone with the following sequence:
1 - Power off Apple Watch
2 - Power off iPhone
3 - Power on iPhone
4 - Power on Apple Watch
Be sure you've waited for each step to complete before proceeding to the next one. If you haven’t restarted the devices before, here’s how: How to restart your Apple Watch. Restart your iPhone, iPad, or iPod touch.
If the workouts are still pausing complete the following seven steps in this article:
Get the most accurate measurements using your Apple Watch. Be sure to work through all seven, by doing so you're double checking none have been missed. If you’re still having the issue, message back which workout it’s happening with, and if it’s happening in more than one, or only one workout.
Cheers!