What kind of case lube are you using and are you wiping them off before putting powder in them? When I was loaing .223 I would use 2 different toolheads, one for depriming, re-sizing and the other for loading. I would re-size and deprime the cases and then tumble after I was done and before loading up the cases. I had about 30 or so cases that did not work but it was with CCI and or Wolf SRP's. Come to find out there were clumps of powder that has a bad smell to it once I tore them down. I came to the realization that I had sprayed a bit much case lube and it made it inside the case and then the powder clumped up over the primer and when it was struck it did not go bang due to the clump.
If you have a bullet puller I would suggest taking those apart and looking at the powder.