It appears to be a foil, which (as previously stated) was probably displaced during production. If you’ve seen primers produced, it’s an impressive process and done on a tremendous scale. A primer missing it’s foil should fire normally, but may be subject to losing some of its compound if handled roughly enough.
As to the rate of true primer failures, in the course of loading and firing nearly four million rounds, I’ve run across exactly three (3) truly defective primers, all of which were completely missing their compound. Two I caught during loading, and one was loaded by a friend who lost a 600 yard BR match when his last round for record (and his last round, period) failed to fire. We did the autopsy back in the loading room, fully expecting to that he’d forgotten to charge the case. We pulled the bullet and found a complete charge of powder inside. Carefully depriving the case, we found a perfectly formed light cup, a properly placed anvil, and not a speck of priming compound. Yeah, it’s happens,but it’s a damned rare occurrence.
