It is more likely for a misfeed to occur if the ammo did not feed out of the mag correctly due some stacking issue, or the mag spring bound up somehow, and it could have gotten messed up as rifle tried to chamber the round. This can happen even with known good mags. After filling a mag, I will usually tap the back of the mag with my hand just to settle the rounds into place, before using the mag.

I was going to ask if you had lubed the bolt group, however I see in your original post that you stated that you had field stripped and lubed the rifle initially. I have experienced some misfeeds and bent rounds when I was new to AR15's on new rifles which were under lubed.

Perhaps I have been fortunate, I have literally shot thousands of rounds out of a few different AR15's and I have yet to have issues with extractors or extractor springs. Although I do have a couple that are getting a high enough round count for such things to start occuring. Perhaps one did slip through quality control, mistakes do happen, and new parts can be lemons sometimes too.