What you are seeing there are not collections, but genuine duplicate files.
Whether Plex will summarize duplicates under one common poster or not, depends on your agent configuration.
If you once had a different default metadata agent for your library, but changed it later, you can end up with 2 posters side by side of the same movie.
One of the copies will be matched to the old agent and the other to the new agent. For Plex, these are different movies.
If you want them to be shown together, you can either
- ‘Merge’ all those posters which are actually the same movie
- perform the Plex Dance with all those duplicate files at once
