I have all my movies in a \movies folder. Each individual movie is in a sub-folder. e.g. \movies\Movie Name\Movie Name.mkv.
When I browse the library, some of these show up as folders and I only see the artwork when I enter the folder. Others show the artwork at the top level and clicking on it goes straight to the movie page.
Some of this was happening because I also use Emby and Emby adds sub-folders for artwork and such. So the directory structure was like:
\movies\Movie Name\Movie Name.mkv
But I corrected that and I still get folders for some items and poster art for others.
Why the inconsistency?