It does not affect function that I have seen. I have fired hundreds of rounds through my 522 and no issues. I have 4 mags, they all wiggle around like that. It's just an annoyance.
Ok, I just checked 3 mags, the supplied Sig Sauer, a Black Dog, and a Model 1 Sales. Every one has 3/8" sway at the bottom of the mag (unloaded, I didn't check it when loaded). Now, I am 99% sure all mags for the 522 are made by Black Dog, just stamped differently.