YES, I HAVE...
I had that same problem when I first purchased my USP... It only happened with cheaper ammo, but the very fact that it happened annoyed me GREATLY! If you manually pushed forward on the rear of the slide, it went into battery and fired fine.
I am fortunate enough to have a gunshop close by, where the employees are GREAT guys, GLOCK armorers, but HK Lovers. One of the guys pulled his USP45 (his DAILY CARRY piece!) out and removed the barrel. We compared chambers, and noticed a TINY difference in one of the corners of the chamber next to the feed ramp. Sam pulled out his Dremel, and in no time, mine looked exactly like Jim's.
My USP now handles all ammo, even the "Atlanta Arms Ammo" that gave me so much trouble before.
I hope this helps. I know you pointed to the extractor as the culprit, but all I can say is... that's what mine did, and it doesn't do it any more.
Good luck!!