At first it is not very apparent how to clean up your video library (i.e. remove duplicates are deleted items), despite the Update Library button being so visible. (Hint, standard settings mean that the Update Library action doesn’t actually clean the library).
No, to clean your library you will need to go to Settings via the main menu options, and from there head over to the Videos section, and finally the Library option.
The trick here is to then spot the label reading either Basic Settings or Standard Settings, and click on it until it reads either Advanced Settings or Expert Settings.
Once this is done, you can now scroll down the main menu item list and you should spot a item marked Clean library… which wasn’t there before.
Needless to say, clicking it will result in a shiny clean library, free of duplicates and missing items!