I'm having problems figuring out what is causing the sticky bolt issue on my new custom build. I have put about 120 rounds through it since completion. During load development I noticed the bolt get sticky a few times, but not necessarily on hot loads. After finding a good load I sighted in and did some range verification. For the last 20 rounds or so, the bolt has stuck on every round, some to the point that I have to tap the bolt open with my cleaning rod. I don't believe this is a pressure issue, as I have not noticed a heavy bolt lift, and I have backed my powder charge off by 2 grains and still experience the same problem. My thoughts now are that the cause is one of the following:
1- Primary Extraction issue in the action
2- Chamber Issue
3- Bad brass (the brass is Lapua brass that has been fired once and FL resized).

Any thoughts/suggestions on where to go from here?