I’ve just reset my computer and have a fresh install of Plex. Going thru my movie collection, I see that there are a few movies that are not matched correctly. On the menu option for the movie (three dots), almost every time I need to do a match, the option is not there. It does show up if I first click the edit button (pencil). Then clicking the menu option, I get two more options (Fix Match, Unmatch). A little annoying but hopefully this helps someone else.
In order for the main page of the web app to build within a reasonable time, not all properties of media items are initially fetched from the database.
Just click through to the preplay screen of that movie.
Then use the ellipsis . . . up, right
