Sounds like you have enabled Local Media Assets for your library and prioritized it higher than let’s say Plex Movie / The Movie Database.
That’ll result in plex checking the file for embedded metadata (in particular titles).
Overall this should only happen with mp4/m4v files – still it can be helpful to change the agent priorities in Settings > Server > Agents > Movies and scan the library again.
Same as with the title… if your agent settings favor Local Media Assets and your mp4/m4v files have embedded metadata, Plex will associate the Album tag (embedded metadata) as Collection in Plex.
Your Library configuration
If you have enabled Use collection info from The Movie Database in the library’s advanced settings this will automatically create collections for your movies — independent if you have other movies from that collection or not.