Not full list of apps provided in NC instalation; Ring/Notifications not working on Android devices

NextCloud 14.0.3 / Ubuntu 18.04 / Nginx 1.14.0 / PHP 7.2.11

Good day!
Cant solve simple issue. I had installed this wonderful service following instruction described here (with a difference that I had used “stable14”, instead of “stable13”). Then created couple of accounts inside of it, to connect mobile devices for test. And noticed that I have no any notifications and/or ring when I was calling or sent a msg to another device. I had re-installed apps (fdroid =then> github =then> playmarket). And noticed that it shows at launch “Push notification disabled”. Then I checked Demo NC account, which works perfectly - devices are ringing when I call, and receiving a notification when I send a msg.

But I also noticed one strange thing: Apps list on my server not complete at all unlike the Demo Account Apps list. Some of Supported Apps, which marked as “Official” in Demo somehow do not exist in my list at all (e.g. “Notifications” 2.2.1, “Activity” 2.7.0, etc). I mean its “non-downloadable”, there is no any mentions about it.

Any idea? Any suggestions? Does anyone have same issue? And how to fix notifications? Please help!

I really liked this service and idea of it uses with family and friends.

(2 Edition) PS
I hear the sound when I testing a voice calls; see the picture with video calls; and msgs passes thru the server without any issues. But without any ring/notification (on other device) as well. (

(3rd Edition)
Forgot to mention Nginx version )