My XD9 has worked flawlessly for me, and I have yet to hear any reports about factory magazine failures.
Also, keep in mind that ProMag is not made with the same quality as the factory XD9 mags. ProMag is a decent company, and they make some decent hi-cap magazines, but they are cheaper for a reason.
When holding the XD9 with a standard "high hold" I cannot get my fingers to conflict with the slide stop, but that's just me. How are you holding your XD9?