A.) Check the cases.
A.1.) Could be the way in which the primer pocket was prepared. Cutting "just a tiny bit" too deeply, or the accumulation of cutting over many uses of the same case, and the primer takes two (or more) strikes to go off. Segregate and destroy those cases (if any).
A.2.) Double check the depth of the primer pockets. Use a stiff bristle brush to clear out the crud, and ONLY "cut into" a primer pocket one time, the very first time, on new brass, for uniformity. Assure that the cutter is not set too deeply, and the cut is not off axis. Segregate and destroy those cases that did not fire.
A.3.) Annealed cases, with unintended soft primer cups, tend to resist the force necessary to set the primer off. Segregate and destroy those cases (if any)...
A.4.) When in doubt, start with NEW brass.
B.) Check the mechanism.
B.1.) Investigate the firing pin (mic it for certainty).
B.2.) Check firing pin free travel.
B.3.) Use oil sparingly. Graphite is your friend. Powder residue tends to accumulate there.
B.4.) When in doubt, purchase and install a new firing pin and spring. They are, relatively speaking, cheap insurance...
B.5.) IDK how to check the hammer and its spring for firing energy and tension, but these could be suspect.
B.6.) Considering there are quite a few machined pins in the mechanism. Pins wear, and could be suspect if the gun has been fired A LOT.
C.) Change primer Mfg.
C.1.) Primers, though rising in cost, are one of the least cost consumables, but the most important element in the BANG.
C.2.) As a last resort, and in the future, move on to a different Mfg.