Cannot connect to Jitsi from most hosts

Hi, everyone
Just installed jitsi on Ubuntu Server 20.04 and configured for LDAP auth with MS AD. Works fine fore some hosts, but most of them cannot connect to Jitsi server, browser says “Server unexpectedly closed connection” and in the error log of nginx I can see error line saying

2020/06/02 11:39:41 [error] 25592#25592: *15 connect() failed (111: Connection refused) while connecting to upstream,

client:, server:, upstream: “”, bytes from/to client:0/0, bytes from/to upstream:

This error repeats with every attempt to open Jitsi login page from the browser. Again, for some hosts Jitsi works fine, but for most hosts even from the same subnet ( in the example) does not. I even cannot figure the dependence rule…

Can anyone help me? All configs (except AD auth) were intact from default installation, but if any configs and / or logs needed, please let me know.