Just getting a movie to the point of completion is an arduous mountain to climb in the first place, so it’s crazy to think that sometimes a director is heavily responsible for a film without ever getting the credit their work deserves.
If they're employed as a sort of puppet-master behind-the-scenes or come in to salvage a project when there’s a vacated directors chair they tend to only be considered a ’ghost director.'
And while their names remain hidden, sometimes uncredited party is more responsible for the final result than the filmmaker credited. Gareth Edwards certainly had some guidance and re-writes on Rogue One via Tony Gilroy, even if Edwards still stands by the final product.
These days, publicity around such changes makes the required air of secrecy for a 'ghosted' movie less likely. The recent case of Justice League is a good example, as original director Zack Snyder left with majority filming wrapped, then Joss Whedon came in, rescripting and directing reshoots for the final project. The entire ordeal was done with such transparency it's difficult to make a case for its inclusion.
But there are other examples that fit this strange mandate where a second filmmaker called the shots yet remains forever an invisible presence in the credits.