Jitsi: Users do not see/hear each other

Hi!
I followed the guide (CT 12/2020) to add user restrictions to jitsi.
It works as far as I can set an admin user, I can log in with that user, set a password to a created room and join with a second client.
But each user (admin or guest) can only see her/his own video.
What am I missing?
Ubuntu 20.04, 19.10 and 18LTS act alike, even when setup completely from scratch.
It worked in 19.10 without passwords...

Start with the CT 12/2020 guide and reproduce the password-protected Jitsi setup on Ubuntu 20.04, 19.10, or 18 LTS using an admin and guest client. Compare it with the previously working setup without passwords and gather the relevant Jitsi configuration and logs. Done means both clients can see and hear each other with room passwords enabled.

Written by the indexing model from the issue text.