Subnautica 2's 4-player co-op mode is one of its headline features, but connection issues can prevent players from joining or hosting games. The most common error is the "Invite Failed" message, which appears when a player attempts to accept a game invitation but the connection cannot be established. This error is typically caused by version mismatches between players, network configuration issues, or conflicts with the Steam or Epic Games overlay. Another frequent problem is the "Lobby Join Error," which occurs when a player can see the lobby but cannot connect to it, usually indicating a NAT (Network Address Translation) issue or a firewall blocking the connection.
Version mismatch is the most easily resolved cause of connection failures. Subnautica 2 receives frequent updates during early access, and if one player has a newer or older version than the host, the game will refuse to connect. To check your version, look at the bottom-right corner of the main menu screen. All players must be on the exact same version number to play together. If versions differ, the player with the older version should restart their game launcher to trigger an update, or the host can verify their game files through Steam to ensure they have the latest patch.
Another common issue is the "Session Not Found" error, which occurs when the game cannot locate the host's session on the matchmaking servers. This is often caused by server-side matchmaking problems that resolve themselves within a few minutes. If the error persists, both the host and the joining player should restart their games and try again. In some cases, the host may need to create a new session entirely, as corrupted session data can prevent new players from joining even though the host can play normally.
The "Disconnected from Host" error, which occurs mid-session, is typically caused by network instability or the host's connection dropping. If this happens frequently, the host should check their internet connection stability and consider using a wired Ethernet connection instead of Wi-Fi. Players on university or corporate networks may also encounter connection issues due to restrictive firewalls that block the ports Subnautica 2 uses for multiplayer communication.
Common Multiplayer Connection Errors
Subnautica 2's 4-player co-op mode is one of its headline features, but connection issues can prevent players from joining or hosting games. The most common error is the "Invite Failed" message, which appears when a player attempts to accept a game invitation but the connection cannot be established. This error is typically caused by version mismatches between players, network configuration issues, or conflicts with the Steam or Epic Games overlay. Another frequent problem is the "Lobby Join Error," which occurs when a player can see the lobby but cannot connect to it, usually indicating a NAT (Network Address Translation) issue or a firewall blocking the connection.
Version mismatch is the most easily resolved cause of connection failures. Subnautica 2 receives frequent updates during early access, and if one player has a newer or older version than the host, the game will refuse to connect. To check your version, look at the bottom-right corner of the main menu screen. All players must be on the exact same version number to play together. If versions differ, the player with the older version should restart their game launcher to trigger an update, or the host can verify their game files through Steam to ensure they have the latest patch.
Another common issue is the "Session Not Found" error, which occurs when the game cannot locate the host's session on the matchmaking servers. This is often caused by server-side matchmaking problems that resolve themselves within a few minutes. If the error persists, both the host and the joining player should restart their games and try again. In some cases, the host may need to create a new session entirely, as corrupted session data can prevent new players from joining even though the host can play normally.
The "Disconnected from Host" error, which occurs mid-session, is typically caused by network instability or the host's connection dropping. If this happens frequently, the host should check their internet connection stability and consider using a wired Ethernet connection instead of Wi-Fi. Players on university or corporate networks may also encounter connection issues due to restrictive firewalls that block the ports Subnautica 2 uses for multiplayer communication.
Cross-Platform Play Issues and Fixes
Subnautica 2 supports cross-platform play between Steam and Epic Games Store, allowing players on either platform to join the same co-op session. However, cross-platform play is not enabled by default and requires explicit configuration. To invite a player from a different platform, the host must enable cross-play in the session settings before starting the game. This option is found in the multiplayer menu under "Session Settings" and is labeled "Allow Cross-Platform Players."
Once cross-play is enabled, the host can generate an invite code that can be shared with players on the other platform. The joining player enters this code in the "Join by Code" section of their multiplayer menu. Note that friend list integration does not work across platforms, so you cannot simply invite an Epic Games friend from Steam or vice versa. The invite code system is the only way to connect players across platforms.
Cross-platform play is not supported with console versions of Subnautica 2. If you or your friends are playing on Xbox, PlayStation, or other console platforms, you will not be able to join PC sessions. This limitation is due to differences in the multiplayer infrastructure and certification requirements for console platforms. Unknown Worlds has not announced plans to add console cross-play in the current roadmap.
A common cross-platform issue involves voice chat not working between Steam and Epic Games players. This is because each platform uses its own voice chat system, and the cross-platform integration does not bridge them. To work around this, use a third-party voice communication application such as Discord, which works regardless of which platform each player is on. Text chat within the game does work across platforms, providing a basic communication fallback if voice chat is unavailable.
Network Configuration: NAT, Ports and Firewall
Network configuration is the most common cause of persistent multiplayer connection issues in Subnautica 2. The game uses peer-to-peer networking for co-op sessions, which means the host's network configuration directly affects whether other players can connect. If the host has a Strict NAT type, joining players will frequently encounter "Lobby Join Error" or "Connection Timed Out" messages. To check your NAT type on Windows, open the Xbox Console Companion app, go to Settings, and look at the Network Status. Open NAT is ideal, Moderate NAT may work with limitations, and Strict NAT will prevent most players from joining.
The simplest way to improve your NAT type is to enable UPnP (Universal Plug and Play) on your router. UPnP allows Subnautica 2 to automatically open the necessary ports without manual configuration. To enable UPnP, log into your router's admin panel (typically accessed by typing 192.168.1.1 or 192.168.0.1 into a web browser), find the UPnP setting (usually under a "Security" or "Advanced" section), and toggle it on. After enabling UPnP, restart your router and computer, then test the connection.
If UPnP is not available or does not resolve the issue, you can manually forward the required ports. Subnautica 2 uses the following ports for multiplayer: UDP 7777 (game traffic), UDP 27015 (Steam matchmaking), and UDP 4380 (Steam auxiliary). To forward these ports, access your router's port forwarding section and create entries for each port, directing them to your computer's local IP address. To find your local IP address, open Command Prompt and type "ipconfig" (without quotes), then look for the "IPv4 Address" under your active network adapter.
Windows Firewall can also block Subnautica 2's multiplayer traffic. To check, open Windows Security, go to "Firewall and Network Protection," and click "Allow an app through firewall." Ensure that both "Subnautica2" and "Subnautica2EAC" are allowed through the firewall for both private and public networks. If you are using third-party antivirus software with its own firewall, you may need to add exceptions there as well. As a temporary troubleshooting step, you can try disabling your firewall entirely to see if it resolves the connection issue, but always re-enable it afterward for security.
Steam and Epic Games Overlay Fixes
The Steam and Epic Games overlays can interfere with Subnautica 2's multiplayer functionality, particularly when using the invite system. The overlay hooks into the game process to provide features like the friends list, chat, and in-game browser, but these hooks can conflict with the game's own networking code. If you are experiencing "Invite Failed" errors, disabling the overlay is one of the first troubleshooting steps to try.
To disable the Steam overlay, open Steam, go to Settings > In-Game, and uncheck "Enable the Steam Overlay while in-game." For Epic Games, open the launcher, click your profile icon in the top-right corner, go to Settings, scroll down to Subnautica 2, and toggle off "Enable Epic Games Overlay." After disabling the overlay, restart the game and attempt to connect again. If the connection succeeds, the overlay was the culprit, and you can try re-enabling it after the session has started, as the conflict primarily affects the initial connection phase.
If you rely on the overlay for voice chat or other features and do not want to disable it entirely, try the following alternative fixes. First, verify that the overlay is running as administrator. Right-click on Steam.exe or EpicGamesLauncher.exe, select "Properties," go to the "Compatibility" tab, and check "Run this program as an administrator." This resolves permission conflicts that can prevent the overlay from properly injecting into the game process.
Another overlay-related issue involves the Steam Input system, which can interfere with controller functionality and, in rare cases, multiplayer connectivity. If you are using a controller, try disabling Steam Input for Subnautica 2 by right-clicking the game in your Steam library, selecting "Properties > Controller," and setting the override to "Disable Steam Input." This is particularly relevant for players using DualSense (PS5) or DualShock 4 (PS4) controllers, as Steam Input's translation layer can cause unexpected behavior. After making any overlay changes, always restart both the game and the launcher to ensure the changes take effect.