I know that the answer is comming too late but it could help others at least.
Your features string CPXP-VPX-250-NG is definitely an NG license (NGX version has NGX string at the end) but it is an "Express" license type (the string CPXP) which was a new licensing scheme introduced after releasing the NG AI R54. To be able to use the NG FP3 and NG AI R54 versions with the Express licenses you must install the
Check Point Express hotfix. The newer releases (NG AI R55, R55W, NGX R60 etc.) recognize the Express licenses natively.