This is happening to me as well on a single player save.

Can't reproduce with a minimal mod list (harmony, core, Setup Camp). Going to need a bug report, preferably in the dedicated discussion.

I'll try and see if I can get around to creating a proper bug report, but I believe it's an interaction with the Multiplayer mod (was able to reproduce with harmony, core, multiplayer, setup camp)

@Kas, I was able to safely remove the Multiplayer mod from my game and it updated the camps automatically to 'abandoned', removing them from the top of my screen. So a temporary workaround would be removing that mod either completely or every once in a while to fix the camps. I would make backups of your save though just in case

I also get this issue when using the MP mod. How did you load your multiplayer save after removing the multiplayer mod?

When I use the Multiplayer mod, the people leaves, but the camp doesn't close

For people searchin the easy solution:
Use Dev mode - "Destroy Map" command. Just destroy unwanted camp site