This is may be because your Apple Health permissions aren't setup correctly. Please double check them by going to the Health app on your iPhone, then select the Sources tab. After tapping on MySwimPro, be sure that ALL of the requested permissions are granted.
If Health permissions are correctly enabled but you are still experiencing the issue, please make sure you are on the latest version of watchOS - you can find instructions for updating your Apple Watch here.
If you are on the latest version of watchOS and still experiencing issues, please try restarting your Apple Watch.