If you are looking to to solve this permanently within the game's code, consider implementing UDP Broadcasting :
: The game underwent a major "Seamless World" update that replaced the old island-hopping system. Ensure all players are on the same version (Stable vs. Alpha/Beta) via Steam properties.
: The most reliable way to connect is through the Steam Overlay (Shift+Tab) rather than manually entering IP addresses. Developing a Native LAN Discovery Feature
: The Client's "Join LAN" menu should listen for these packets on the local subnet.
The "Craftopia Fix LAN.rar" file is likely a community-made patch or mod designed to bypass multiplayer connectivity issues, particularly for users on older versions or those attempting to play via Local Area Network (LAN) emulators like Hamachi or Radmin VPN. Recommended Official Fixes
: Program the Host machine to send a "Heartbeat" packet every few seconds on a specific port (e.g., 8788) containing the Server Name and Internal IP.