No background notifications on iPhone called from Android Riot

A friend, Harry, has Riot 0.6.6 master #102 and when it is not in the foreground the app does not notify messages nor ring on incoming calls from my Android tablet running 0.7.04 (from Play Store). Harry has activated all the notification options that he can find on his iPhone MP822X/A running iOS 11.1.2 (15B202). When Riot is in the foreground it rings. When Harry has riot open on PC Windows, the PC rings.

When I ring Harry from my Android phone running 0.7.03 (from f-droid), the same problem is the same.

When another iPhone running Riot 0.6.6 calls Harry's iPhone, Riot shows a notification and rings even when it is in the background.

Why does Riot on the iPhone correctly react to calls from an iPhone but not from an Android phone?

When I ring Joe's iPhone running iOS 11.2.1 (15C153) and exactly the same version of Riot, the call and notifications arrive even when Riot is in the background.

Another perhaps unrelated problem is that when Harry tries to make a video call my Android phone does not ring even then I have the app open. There isn't even a message on Harry's phone saying that a call has been created. Voice calls work fine. Riot.im is authorised to use the camera on Harry's phone. Incoming video calls cannot be accepted even then Riot is open (there is just a message that I've made the call).

Any clues on how I can make Harry's phone ring when I call him? Thanks