Guys I have the exact same issue, meaning when someone rings at my VTO, there is no push notification anymore on my mobile to interact with this person, and this since Upgrade to V4.30 which happened few days ago.
In the past on the old app, there was an option to set like 'Alarm', in order to get notificarions ... now this is hard to find, but I found it :
So version 4.30 :
on the menu on the left, click "Message Center" on the top there is like an enveloppe and a cloud icon .... click the Enveloppe, then the "tag" icon next to it (the icon on the right of the filter). A menu will display the devices, next to the Portier there is a slidebar to "enroll".
Do not ask me why it is like this ... this is stupid, totally NOT user friendly, I wonder why this is there, but enabling this option you will get back the notifications.