Speculation is that that Fox wants to go all out in making New Mutants a horror movie after the success of It and Get Out
http://www.tracking-board.com/deadpool-2-pushed-up-two-weeks-as-new-mutants-moves-to-2019/
Josh Boone’s The New Mutants has been pushed back a second time. It was originally scheduled to open on April 13, 2018, was then moved back to February 22, 2019, and has now been pushed all the way back to August 2, 2019.
NM seems to be the new “Gambit” .