Jitsi Crash after joining the third Person

Hello folks,

i am a Newbie with Jitsi and we starting the first Tests and we run everytime in the same Problem.
We start a Conference with two People and all works (near) perfect. Sometimes it is a little bit laggy but okay.
But if a third Person joins the Meeting, the hole Room crash and the Video of all is dissapeard.

I am using the Jitsi Docker Image ob a Ubunutu Server with 8 CPU, 8GB RAM and my Upload is 40Mbit/s.
I also tried to force the Quality down to 180 in the .cfg but the Streaming from the Clients is allways HD.
We dont need HD Quality for a Talk. Our Goal is to create a Room with 20 People and a small Quality would be enough for us.
But we are not able to invite more as two People now… :frowning:

Thank you very much