I've had two Krytonites and two off-brand U-locks. Never had any issues with jamming.

It seems like you're treating the locks OK. How about the keys? Is it possible you're somehow messing up the profile of the keys?

It sounds like your LBS has been good to you, but it isn't their problem any more.

Send that lock & key to Kryptonite with your story and ask them what's going on. It might be education, or it might turn out to bad quality control.

It might also be that someone is putting stuff in your lock when you leave it with your bike. (toothpicks, sand, etc.)

Beyond that, I'm out of guesses.