Once you pointed it out, I found the LCI to be really stiff. I have fired 1500 rounds at least through this and I think it is probably crud. My plan is to remove the rear sight, dismantle the LCI and clean out the whole thing. While I am at it, I may as well clean out the firing pin mechanism as well since I will be in the neighborhood, so to speak.
This nick, in some cases, was pretty deep. Since once fired brass is so cheap, I discarded those that look too deep and the rest I will clean up and reload, then check to see if my handiwork paid off.