Jisti in a DMZ access from intranet and internet fails

Hi everyone!

First, thank you for the nice community and work !

I run a Jisti Server in a DMZ. Furthermore I used LDAP for authentication. And it works pretty fine.
But there is an issue I do not understand.

This setup works. one Internet actor and one local actor can have a chat:

Also this setup works very well:

and so this works too, all actors have a chat:

But if an internet actor joins the room like this:

everything gets messy.
The local actor loses its connection. They are still in the Room but they neither can hear nor see anything. And so the other way around. If there is a room with internet actors and a local one joins the room, the internet actors lose the connection but they are still in the room.

The fact that makes me wonder is, if there is a room with one local and one internet actor everything is okay, but if a third person joins the room, the local side or the internet side gets lost, but they are still in the room.

My first idea was, okay let the local one access on the external interfaces with the public IP. But that won´t work, as well. I tried different things, e.g I configurated various NAT rules, but nothing happend.

Has anyone an idea?
Thank you so much in advance

Kind regards