If you have the outdoor trait, you would get this: buff_CampingForest_LovesOutdoors_Rejuvenated
For sims without that trait, you would get this: buff_CampingForest_Refreshed
They use the same test condition. I apologize if I didn't include the Outdoor workaround earlier.
You have to remove each buff according to your needs - if you want to. Some may actually like this, since you get a permanent +2 happy.
It happens only if you have ended a vacation early.
I have tested sending Sims on vacation without ending early and the buffs get removed properly (i.e. the decay over time happens).
I think, from what I could understand, when traveling on vacation, your Sims in the group get tagged with an unique number. This ID will be marked for removal properly if the vacation is ended properly. If not, the ID persists and gets saved in your Sim data. So, each time you go through a loading screen (e.g. load from a save, switch between neighborhood), there's a chance the buff will return because that travel ID has not been removed. The workaround just takes out the buff not the travel ID.
So, if you send Sim A,B,C on a vacation previously and end it early, all Sims A,B,C get stuck with the ID.
Next time, if you send the same Sim A,B,C with a new Sim D and end the vacation normally, only Sim D gets the buff removed properly (tested).
Since evict, moving out household works with the same save file, it won't help (tested).
What I have not tested is, what would happen if you send the same Sim A,B,C back to vacation and end it properly?