1. Confirm the server is actually using crossplay
Iron Gate's dedicated-server guide says the -crossplay argument switches the server to the PlayFab crossplay backend. Without it, the Steam backend is used and only Steam users can see and join the server.
2. Use a fresh Join Code
Iron Gate's crossplay FAQ says hosts can copy a Join Code from the pause menu and players can paste it through Join Game → Add server. If a code stops resolving after a restart or patch, generate a new one before changing the world or reinstalling everything.
3. Do not test a crossplay server through a local/loopback IP
The official dedicated-server guide says crossplay servers use a relay backend and cannot be joined through a local IP or loopback address. Use the public route, server list or Join Code instead.
4. Check patch timing before touching the save
Valheim 1.0 is still receiving frequent hotfixes. Patch 1.0.14 noted that platform uploads can arrive at different times while crossplay remains supported. If one platform suddenly fails, first confirm every client/server has received the current compatible build.
5. Separate server problems from one-client problems
If several players on the same platform can stay connected but one player is kicked, treat that as a client/account/cache path first. If every console client fails while Steam works, inspect the server backend and current patch status first.
Official references
Dedicated Server Guide · Crossplay FAQ · Patch 1.0.14
Unofficial guide. Product and game names belong to their respective owners. Always check current official patch notes before changing a server or important save.