It was recently reported that Fox pushed the release dates back for X-Men: Dark Phoenix and The New Mutants. We won’t be seeing these films released until 2019. Thanks to Collider, we now know the reason for the delay and that reason is because of some reshoots that need to happen.
X-Men: Dark Phoenix was originally scheduled to be released on November 2, 2018 and was moved to February 14, 2019. The New Mutants moved from February 2019 to August 2, 2019. This is the second time that the release date was pushed for that movie. It was originally set for an April 2018 release before being pushed to February.