New Mutants is a different matter, however. When the film was initially delayed, it was reported that Fox wanted to do some reshoots to make the movie scarier, even going so far as to add a new character. That still holds true, and while we hear the film tested well, it’s not “scary” enough. Director Josh Boone delivered a cut of the film that he was happy with, but Fox wants this movie to stand out as tonally distinct the same way Logan and Deadpool did.

The reshoots that the studio wants are now even more significant. We’re hearing that at least 50% of the movie may be reshot, and they’re adding one or two new characters who will be present throughout the entirety of the film—this isn’t simply adding a cameo. Moreover, Boone has been having some creative differences with the studio over the requested changes to the movie, so the reasons for the New Mutants delay are more complex than why Dark Phoenix is being pushed.

http://collider.com/x-men-dark-phoenix-new-mutants-release-date-delay-explained/#fox