This bug has been well and truly squashed in app version 3.49. The new version is available in the app store.
We are currently aware of an issue on iOS devices where users are unable to cause their phones to ring by pressing the button on their Finders. We are working diligently to address the issue and will post an update here when a fix is available.
If you would like to receive an update once we post it, please 'follow' this post above.
We apologize for the inconvenience and thank you for your patience.