Hadn't thought about that but a very good theory. You never know how consistent they are in loading some of this ammo from BFE or wherever. I've got some lithium grease I'm going to try on the rails on its way. I don't think I'm going to try any of the 15 round magazines. I do have 4 of some kind of unmarked generic 13rd that I'm not sure about just yet. Good ammo on the way and I believe this will make a world of difference.This could easily be from the ammunition being weak, and not pushing the slide fully rearward to the end of it's travel. Especially on a tight, new full sized 9 MM pistol. This will for sure cause failures to feed, as well as eject. It's crucial the slide operate through it's full length of travel each and every time the weapon is fired. And with enough velocity and authority to cause the weapon to cycle properly. Try a couple of boxes of quality +P ammo, and grease the frame and slide rails good. I'm willing to bet that will fix your problem.
Mec-Gar magazines are top shelf. And the 13 rounders in the Hi-Power always feed the best, because the followers are longer. On the 15 round models, they require shortening the followers in order to get the extra 2 rounds in. This can sometimes cause feeding issues in some Hi-Power models, because it allows the followers to tilt and cant, which can cause a FTF.