The Goblet of Fire introduces a ton of new and exciting things with the world building of Harry Potter, including a bunch of issues, solidifying that JK is just making this up as she goes.
The issues have become glaringly apparent upon a reread, like how come they are never mentioned again, where have they been so far? The Big Picture things.
But one thing I think JK does exceptionally well for World Building are the Small Picture things. Like the newspaper or sports. Things that make the small picture we have feel so alive.