Update 2025/01/30
EA has implemented a non-fix for this. This means that the items are no invisible (most of them) but still there. The overlapping festivals seem fixed but the objects are not....
Ideas
I still see loads of items that don't belong in the household.
Can even still duplicate it the same way with S4Studio. The festival main objects are gone but I still have plants and snowglobes, etc.
I still can see canoes in Sulani but e.g. no plants in my households there. And like you said they keep duplicating.