Jitsi Android app not working from within LAN

Hi there,

I have set up Jitsi Meet with docker-compose set-up and everything works fine from within LAN or from WAN. The error I encounter is, that when trying to connect with the Android App from local Wifi there is no connection established. Using the App without Wifi enabled, using GSM, everything works fine. Connecting from Smartphone using the browser in desktop mode is working fine in LAN and from WAN, too.

Setup looks like this:

Local VM running on Ubuntu with Jitsi docker-compose setup.
FQDN set up and NAT setup for port-forwarding.
nginx as reverse proxy working correctly.
Lets-encrypt certificates working correctly (see https://www.sslshopper.com/ssl-checker.html#hostname=meet.bunter-block.org)
DNS override to local server for local reqeusts to FQDN
SSL Certificate is handled by nginx

The only hint I found in the Forums was https://github.com/jitsi/jitsi-meet/issues/3210#issuecomment-404086168
But I don’t know what it means to do.

Someone any idea for solving or debugging?

Thanks in advance

Edit: I tried with a different phone and there it works without problems. So the problem is just with some phones.