Hello, is stuff created with max creation graph 2016 compatible (after "compiling it" into modifier or script) with older versions of max, which ones? 2015,2014,2012...?
Next thing I would do is duplicate the problem mesh, delete history, do a humanIK quick bind and then export that and test it in engine. If that works correctly, then you know the problem has to do with the mesh itself rather than the import/export process. If this is true, then I'd probably start by copy the current skin…