Interesting. Not an issue I've heard of.
We can assume that you have already stripped the gun down an inspected the slide, barrel, guide rod, mags and rails for signs of abnormal pressure / rubbing -- yes?
I would take the barrel out and see how the slide alone feels on the rails. Then would closely inspect the mags to see if there is a conflict there. My best guess is that there is an issue with the guide rod. The ones of that design are not eternal and they can wear out. A call to SA may shine more light on the cause / solution -- but may require shipping the gun in.