I've had consistent FTF problems with ProMags in my SIG P229/.40. I have never had so much as a hiccup with factory mags. The problem appears to be weak springs, and perhaps the feed lip configuration.
Some folks have had good results with ProMags right out of the box; others have been able to tune up defective mags; still others can't get them to work no matter what they do. My experience has been that it is not worth the time and money needed to correct them. The best that can be said about ProMags is that they are a gamble -- sometimes you win and sometimes you lose.