I'd contact S&W. They should send you a call tag for return at their expense. Who knows why? It seems odd to me that only 3 of 6 chambers are affected.
Over the years, I've had 3 329s (still have 2) and have shot 8,000 or 9,000 rounds total thru the three (over 95% mostly A2400 with some H110). Had various problems that required a return to the factory for repair. I never had a problem with cylinder face erosion as shown in your picture.
Who knows why this happened. It could be a factory defect of some kind (uneven ti coating maybe). Could also be related to your cleaning method or products, or even have something to do with the powder used in the PPU ammo.
Here's a picture of a cylinder with a lot of rounds (don't remember exactly how many) -- this is the way all three guns look(ed).
May be an inconvenience, but S&W should take care of your problem.