Larian stated that its a problem they are investigating. So be patient.
What you can do however is what I and my friend did when we wanted to play together on saturday.
Use vpn based app
https://www.evolvehq.com. Follow the instructions how to set it up and you will be able to play with your friends on a LAN through vpn connection. Its free and a solution until Larian fixes the problem.
Enjoy
