Can’t play two people from the same IP

The game won’t let two of us play from the same public IP. As soon as the second player connects, it kicks one of us back to the main menu. Priority always goes to whoever joined first. We also can’t bypass it by playing outside of a party—same outcome. Bottom line: only one person on our network can play at a time.

Can you confirm if this is a known restriction or a bug? If there’s a workaround (settings, ports, UPnP, anything), please share. Thanks!