I had a few 20 round PMAGs that felt a little less than perfect. I pulled them apart, and found a TINY bit of flashing on the back of the follower. Even though it did NOT seem to be enough to make a difference, I trimmed it, and threw it all back together. Once reassembled, it felt quite a bit different.
I should point out that I fired well over 2,000 rounds through 20 round PMAGs over the course of a few days, and there was no functional difference between the ones I played around with, and the ones I left alone. No difference in semiauto firing, no difference in suppressed firing, and no difference in fullauto firing.