Friend gets bad password error when entering caves?

[Cola No Pepsi]

I've been hosting a DST world with my friend and I, and we've been playing normally for about 80 days now. I had already entered the caves a few times, but my friend entered for the first time today and received a bad password error upon entering, as well as a bad password error every time he enters the server. I've been able to rollback the game a few days to pull him out of the caves and stop the error, but entering the caves seems to start the issue again.

I'm not running a dedicated server, it's just through steam. All don't starve together apps are allowed through the firewall. I've disabled mods. Really not sure why it's only happening with caves thus far.

[Orangex]

Are you actually using a server password?

If so you could try removing the password then setting the server to friends only and 2 players only. This way you don't have to worry about a password and it still acts like a private server for you and your friend.

[Cola No Pepsi]

Originally I was using a password, but I have since removed it. Even then, he's still getting the bad password error when entering the caves.

I also forgot to mention in the original post, but the server has always been on friends only, 2 players.

I'm just confused as to why it's only the caves which are causing issue for him.