Problems joining a lobby?

If you have problems joining a lobby, you should check if UPnP is disabled in the router. You should also check whether it is not possible to use another network (e.g. use a hotspot on the smartphone). There should also be no custom firewalls or other security solutions. If in doubt, deactivate and / or uninstall and test. If this is successful, you will have to make the appropriate configurations or do without these solutions.