I also had a problem with one of my XDm9 19-rd. magazines - it was one of 6 that I bought directly from Springfield, taking advantage of their sale (for those wondering why I got mag-crazy: "New" XDm9 from Cleveland - POA/POI & magazine questions
No jams: but the slide was locking back on every round.
I was *this* close to sending the magazine back to Springfield, but after a strip and reassembly, and after cramming it up to-capacity - magically, it cured itself.
I've several different factory ammo through it: Winchester "White Box," Speer Lawman and Blazer, just to name the more affordable ones, and that magazine no longer hickups.
I don't think I'll ever trust that magazine, for SD/HD - so I have it clearly marked on the base-pad for range use only. I guess my advice would be, oldschoolhd
, for you to do a strip and reassembly of the magazine, load it up to capacity, unload (manually, if you wish) - and repeat perhaps once or twice more, and see if things don't just settle in.
But that's assuming, of course, that the problem is magazine related.