Real world story: I was doing a lot of matching of unmatched movies and I accidentally clicked on a wrong search result in the Match dialog and I have mismatched a movie. I cannot find it anywhere. I tried to rename the file, hoping that it will pop up as unmatched again - no luck.
I think a filter option “Recently matched” or a possibility to search movies by file name would be a great time saver in PMS.
Explore “Duplicates” - as that is where mismatched Merges go to be hunted down and Split… or have their names fixed. You’ll need to Get Info on the possible candidates until you find your item.
Lacking that filter option, this might be a way to fix it:
Rename the file’s extension to something Plex won’t recognize as a movie file.
Scan Library files so Plex removes the movie from the library.
Rename the extension back to its correct name and scan library files again so Plex will re-add it.
It should be unmatched again, or correctly matched if Plex does better than the first time. Sorting by ‘date added’ would make it easy to find, if necessary.