Hey Alex…
Just another small issue.
When you have the app open on the phone and the phone is in portrait mode whilst using airplay to the Apple TV.
Select the workout…
Rotate the screen to landscape still whilst in airplay to the TV.
The app crashes every time.
I’ve had it work if you open the app whilst in landscape orientation then connect it to the Apple TV.
It also works ok if you are not using airplay to the apple TV. (Just tested it)
So I think the issue is going from Portrait to Landscape whilst connected to the Apple TV via Airplay.
Any questions just ask as Im not sure if that makes any sense 
James