I had a different issue, but this is the process to reset the sensors the CSR walked me through I called in.
On your phone:
Settings >> Apps >> Galaxy Wearable >> Force stop. Then Storage >> Clear Cache.
Then go back to Apps and follow the same process within the Samsung Health App
Go back to Settings >> Battery and Device Care >> Optimize now.
Once that completes turn off your phone and leave it off for a minimum of 3 minutes. Reboot your phone and see if it's working now.