Modern multi-core processors can sometimes cause the game engine to "stutter" or freeze online.
Go to the multiplayer menu and select instead of Online/Steam Matchmaking.
: One player must create a private network and share the Network ID/Password with the crew.
Click the button next to "Clear download cache".
Traditional port forwarding is becoming obsolete with modern routers. Services like or Radmin VPN trick your computer and your friend's computer into thinking they are on the same local network. This completely bypasses Steam's proxy issues and NAT restrictions [14†L21-L28】.
If you cannot join friends specifically, your Steam client might have desynchronized, causing matchmaking to fail. Completely . Re-launch Steam and allow it to log in and sync.
