primers not seated tight or excessive FL sizing
I would say lube on primers if they hadn`t fired second time,,,could be a thin lot of primers also,,or some brass thats been overloaded,,I`d try it again with different bras and primes..
Likely. I'd also say firing pin dragging but it wasn't that cold this afternoon. Mr. big's probably right. I vote for oversizing. I like to have them where I can just feel a little pressure when closing the bolt so I know I don't have that little bit of headspace that can cause this problem. My namesake the 35 Whelen is notorious for this problem and I have to watch it like a hawk. My Ruger and NEF both have long chambers and you can't let the dies full length size and bottom out the press on the die or you'll get a nice click when you pull the trigger.
Take the firing pin out of the bolt and then try the brass to see what the fit is. It'll be a little safer that way. You'll still have the drag of the ejector spring but slowly adjust that die in until you can just close the bolt on a sized case. It's worked for me in the past. Good luck.