Could be because you handled the primers with lube on you hands. That would be my guess too. Also you mention a lube mat. I am assuming you are using the RCBS lube and pad.I pitched mine many years ago because it was to easy for me to get way to much lube on the cases. And you must remove all the lube on the brass before loading it into a chamber less you want to take a chance on building dangerous pressures. When you lube the inside of the neck,you don't need a lot of lube. Don't overlook cleaning your dies either,dirty dies will lead to hard working. Sometimes during the sizing process,I'll shoot a short spray of spray lube up and into the sizing die for easier sizing. I have a friend that won't use Wincher primers. He hates them because he had to many not go off. I have use3d them off and on since 1970 and I haven't had any problems. Which brings me to yet another possible reloading problem. You might not be seating the primer all the way . If it is not seated into the primer pocket all the way,it will move forward on contact with the firing pin which lessons the force required to ignite it, hence,misfire. I hated cleaning the lube off of the brass also so I have a devoted case vibrator just for cleaning the lube off. I believe that " do not handle primers with your hands" is printed in every reloading manual. Must be a reason. I think the manual might be telling you," I told you so".