My Shield 9 was a PC (Problem Child). Not sure why, but I always got the same CSR, and we went through sending it back for feed and extract/eject issues four times.

The CSR (I'm not naming names) got frustrated when I had hit 2k rounds, and having multiple shields in his family, took it to the test range himself (I think he was sure I was an old crazy guy), but sure enough, even after the fourth "repair" it failed on him. He took it to a Sr. gunsmith, and he came to the decision that it was a barrel issue. After some work, they finally changed the barrel for one from a new batch, and replaced the slide.

It is now perfect.

I suppose I should have given up earlier, but about 2k perfect rounds later, I've tended to forget all that.