Personally, it sounds like a magazine issue to me. I have a pre-ban P226 and the only lockups I have ever experienced are with new shooters limp-wristing it. I have literally fired better than 10,000 rounds and never had a gun-related malfunction...and this with everything from CCI Blazer to Cor-Bon and everything in between.
Assuming you have two magazines, put a piece of tape or something on one of them so you can differentiate one from the other. Go pick up a couple of boxes of that ammo you're having issues with and fire a box through each mag. If it happens with both mags, it's time to send it off to SIGARMS. However, I suspect it's simply a mag issue that can be easily remedied with a new mag. Excellent condition factory P226 hicaps can be had for as little as $35 if you look around carefully.
Good luck!