Had same problem.
I disassembled the mag completely. Checked all of rings and all were intact. I worked from bottom to top. Reassembled all of rings with silicone grease. Worked on top end where "firing pin" is held in with spanner nut. Disassembled, inspected and reassembled with silicone grease. Tightened spanner nut with small, angled needle nose pliers. I tested each o ring section with a cartridge. The problem ended up being the firing pin seals. The silicone grease took care of it.
I oiled the mag and gun with silicone oil.
It now runs BETTER than new.
Hope this helps.