One player cannot join our Lethal Company server while everyone else can

A Lethal Company server appears online but one or two players cannot join. Restarting everything only helps randomly.

How can version mismatch, mod mismatch, NAT, and corrupted local data be ruled out without wiping the world? The setup includes microphone detection, mod-free testing, host migration, and Unity crashes.

Check host and client in the same order:

1. Confirm identical game versions.
2. Remove all mods for a clean test, including server-side dependencies.
3. Verify files on the player who cannot join.
4. Test a direct invite and server-browser join.
5. Check host firewall/NAT and confirm the server port is actually listening.
6. Back up the world before changing server files.

For Lethal Company, pay attention to microphone detection, mod-free testing, host migration, and Unity crashes. Do not wipe the world until a new empty test world proves the save itself is the problem.