Message: Lost connection to signaling server in talk - What is wrong?

Hi nextcloud - Community ,

I use 19.0.3 (I will update soon)
Talk 9.0.4
Debian (latest)
php: 7.3.19
apache2 latest
Firefox 63.0.1

I ususally can use nextcloud without problems but there is an issues that my colleges and I cannot connect via talk conference but another one can. I am trying to dig into that but unfortunately the log files (in Debug mode) do not even mentions this.

I guess that something is blocking after a short time and every 5 seconds a reconnect is tried. Could that be true? And if that is true could it be a firewall blocking?

Here a picutre from wireshark and Debug Konsole from Firefox:


If neccessary I will try provide apache log and nextcloud config too because that is a bit tricky.

Thank you!