Apple watch/UA Record App/Polar Beat HRM

I Wondered if anyone could help me?

I recently bought an Apple Watch mainly as a fitness tracker.

I wasn't overly impressed by the HR readings and my overall workout values so I bought a Polar Beat H7 chest strap heart rate monitor.

Because the Apple Watch workout app doesn't breakdown the heart rate zones in the workout, I've been using the Under Armour Record app.

My issue is, the watch doesn't want to constantly read the chest strap.

I'll record a workout and although it has timed me for 50 minutes, it only picks up my heart rate for 20 minutes.

I've spoken with under armour and they're telling me that the watch isn't reading the chest strap properly.

Has anyone else had this issue? Or have any tips on other apps I can use?

Thanks!