CrossplayJoinCodeFix

A server-side fix for Valheim crossplay dedicated servers that run fine but show as offline: nobody can find or join them, although the world is up.

The problem

When a crossplay server starts, it registers a join code with PlayFab and asks PlayFab whether the code is unique. Sometimes PlayFab answers with part of the data missing (no lobby list, or a lobby without its owner). The game does not expect that: it throws a NullReferenceException in ZPlayFabMatchmaking.OnCheckJoinCodeSuccess and never activates the lobby. The usual workaround is to stop the server for a while and try again.

If your server log shows that exception right after start and the server stays invisible, this plugin is for you.

What it does

It checks PlayFab's answer before the game reads it:

• A complete answer: nothing changes, the game's own code runs.
• The only lobby returned is the one this server just created: the lobby is activated, as the game would have done.
• Otherwise: the check is repeated every few seconds until PlayFab answers properly. If it still has not after the timeout, the server registers a new join code and waits again.

The log shows CrossplayJoinCodeFix 1.0.0: join-code check guarded (...) once it runs.

Install

On the dedicated server only, with BepInEx: install it with a mod manager's server profile, or copy CrossplayJoinCodeFix.dll into the server's BepInEx/plugins. Players need nothing.

Settings

BepInEx/config/local.crossplayjoincodefix.cfg, section [JoinCode]:

Setting	Default	Meaning
TimeoutSeconds	30	How long to keep re-checking an incomplete answer before registering a new join code.
RetrySeconds	2	Time between two checks while waiting.

Notes

• Tested on a crossplay test server with simulated incomplete PlayFab answers. The last-resort path (a new join code after the timeout) has not yet been seen in a real outage: reports welcome.
• It only touches the join-code check; servers without crossplay are not affected.

Source and issues: github.com/Shuiei/CrossplayJoinCodeFix