Thanks Eddy. I'm 99% sure that was the problem. I was able to recreate it reliably with undamaged cases before I noticed a small buildup under the extractor on the bolt face. Once I cleaned it the problem went away. These were once fired factory rounds out of an AR platform 6.5 Grendel. I know ARs are rough on brass but I never saw this before. I just started reloading though so it could be I just never looked.