: The default bandwidth limit is often too low, causing desync. Open the console ( ) and type cli_iMaxBPS = 65536 to increase it.
: Set your connection type to LAN in the multiplayer settings, even for online play. This forces the game to use its maximum capacity rather than throttling the connection.
: You must actually load into the level for the server to become joinable. You can select "Wait for all players" to stay on a black screen until everyone arrives.