The core Notification System in UNA is broken and has been for a very long time.  The mobile app and Jitsi were integrated into the broken Notification system and then connected to OneSignal. 

You can not get the UNA mobile App approved on Apple unless you completely turn-off Jitsi and remove all reference to VOIP, incoming calls will not ring.

Here is a brief list of some of the UNA problems: https://unacms.com/page/view-post?id=397

We have been working with the UNA team for weeks now to get these resolved as we were not able to resolve them ourself. I can safely say that the UNA team can not resolve them either and notifications will continue to break your heart, chase users away from your site and disappoint you.