[Jitsi-Docker] You have been disconnected ... Rejoin now

Hi all!
I have a freshly installed Jitsi on Docker. It starts up without any visible error message (just the usual blurb), but when I try to open a meeting I get immediately that error message: You have been disconnected
I tried to do a plain vanilla configuration, so the only things I changed in my env-file are those (besides the passwords):

I replaced my domain with mydomain.com

meeting is the name of the host it is running on

HTTP_PORT=80
HTTPS_PORT=443
TZ=Europe/Amsterdam
PUBLIC_URL=https://meeting.mydomain.com:443
ENABLE_LOBBY=1
ENABLE_WELCOME_PAGE=1
ENABLE_LETSENCRYPT=1
LETSENCRYPT_DOMAIN=meeting.mydomain.com
LETSENCRYPT_EMAIL=mymail@mydomain.at

The logs do not show any error (at least concerning what I get from docker logs …), so i.e the webserver only shows the get requests the client browser is issuing, but no error message. It also does not depend on the browser: neither firefox nor chrome nor safari will work …

So any idea where to start? I can supply you with any information needed, I do not want to flood the forum with potentially unnecessary stuff …