Why does the app have trouble reading my heart rate?
There a few reasons why the app could have trouble reading your heart rate:
First, make sure that your Apple Watch is comfortably snug on your wrist. A loose watch jor too tight watch will have trouble reading your heart rate.
Second, move your watch to the bottom of your wrist during your workout. The Apple Watch reads heart rate via light so by moving the sensor to the lightest part of your wrist you increase the chances of accurate readings.
Third, check to make sure 'Workout Power Saving Mode' is turned off:
Open the Watch app on your phone > click General > scroll down and make sure Workout Power Saving Mode is turned off
Lastly, check that your Health permissions are properly set:
Open Settings on your Apple Watch > scroll down and select Health > click Apps > find and click on the app > make sure all permissions on turned on.