The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
Things I've tried:
Check firewall/antivirus - not the problem.
Reinstall client - still cant start a game.
Full windows reinstall - still can't start a game.
Used a VPN - This fixed the issue. Not ideal but can start and join games.
Hope this helps. Good luck team.