Notifications coming through but no sound

I installed my Ring 2 yesterday, and whilst the notifications come through to the phone ok, and the phone vibrates, there is no notification sound played. I have tried changing the notification sound but still notifications are silent (apart from the vibration). All other notifications from other apps on my phone work as expected and play the notification sound fine. The device is running Android (it's a Xiaomi Mi 8 Pro), and I have tried removing and reinstalling the app, but still there is no notification sounds Anyone have any ideas on how to resolve this? Thanks