With the newly released beta version of Plex Media Server (version 1.20.0), Plex is introducing a new movie scanner/agent. This new agent allows setting a limit for automatically created collections.
If you e.g. have only 1 movie of your favorite collection and set the minimum threshold to 2, Plex will not create that collection (neither as an inline collection inside your library nor within the collections tab).
Example:
Let’s say I have set this threshold to a minimum of 3 movies. So far, I only added “The Fellowship of the Ring” and “The Two Towers” from the “Lord of the Rings” collection to my library. Therefore, the movies will show individually and no collection is being created.
Once I add “The Return of the King” and meeting the minimum threshold for automatically created collections, Plex will create that collection and add all 3 movies.