X-Men: Dark Phoenix marks the directorial debut of franchise writer/producer Simon Kinberg and brings back the star-studded cast of X-Men: Apocalypse, plus Jessica Chastain in a key role. Kinberg’s script convinced A-list talent like Jennifer Lawrence and Michael Fassbender to return even though their contracts for the franchise ran out with Apocalypse, but with A-list talent also comes high-class scheduling issues.

Sources with knowledge of the situation tell us that Dark Phoenix had a test screening to see what was working and what wasn’t, and like most big budget films it needs some additional photography—this is standard procedure for blockbusters nowadays. But given the in-demand nature of this A-list cast, getting all the necessary cast members assembled for reshoots is no easy task. The earliest availability for everyone to return was August or September of this year, which would leave just a couple of months to complete necessary visual effects for the new scenes. That wasn’t enough time, and so Fox decided to push Dark Phoenix’s release date to February to give everyone the time necessary to complete the needed additional photography and post-production on said sequences. So the release date delay for this film is basically just an issue of scheduling.

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