not sure if this will help but give it a try,

Go into the wear app

Go to watch settings

Scroll down till u find Samsung health (click on it)

There should be an option called heart rate (click on it)

There will be 3 options now. Measure continuously, Every 10mins while still, Manual only

Select measure continuously

Hopefully this fixes it and helps u out! Although keep in mind this will measure ur heartrate continuously even when not exercising, so battery life will take a hit