I have had this problem with Kodi many many many times over the years, no idea why.
I remove the item from the library entirely, set the library type to nothing, cancel scanning the folder, clean the database.
Then re-add
Still won't appear - pisses my poor wife off!
She has to go into 'files' mode, NOT 'TV' mode for her shows - they're not in the library.
What am I doing wrong?
Video!