UserProfile.restingHeartRate is 0

Hello.
My latest watchface gets value of resting heart rate from UserProfile.
Works perfect in simulator and on my FR645.
Now I got comments from two users with Fenix 3 HR and VA3 who claim their resting heart rate shows 0 in my watchface.
Any ideas what could be the problem? Could it be wrong setting in user profile on watch or in mobile connect?

var uProfile = UserProfile.getProfile();
var hrRest;

hrRest = uProfile.restingHeartRate;
if (hrRest == null) {
...
}