If you are creating “collection”-type subfolders, you need to adhere more closely to the recommended naming style with its contents. https://support.plex.tv/articles/naming-and-organizing-your-movie-media-files/
Ideally, you create subfolders for every movie within the “collection” subfolder.
I am doing this and it works alright:
If you rename your files, you may have to perform a Plex Dance to clear any mismatches you might have now in your Plex database.
