Fixes
How to Fix Co-op Not Connecting in How to Fish
The single most common cause looks like a network fault, but it isn't one.
Mismatched patch versions refuse lobbies. This is the single most common cause, and it looks like a network fault rather than a version one.
- Make sure everyone is on the same patch, and restart Steam after a hotfix — it will happily keep an old build running until you do.
- Have the host try a fresh lobby rather than reusing the one that failed.
- Only after that is it worth looking at your own connection.
Lobbies run 1–8 players. Friendly fire is on, so a co-op wipe is not always a bug.
Compiled from published troubleshooting guides and the patch notes they cite. Not yet verified on our own hardware. If this stops working after a patch, or you solved it differently, tell us.