having this issue on both my 9mm 1911s. Wilson mags with newer wilson metal followers. wilson extended slide stop. when the last round is fired the follower will either bind up against the side of the stop or slip right up past it and rest on top. this wont allow the mag to drop free which is no bueno in a uspsa match.

any ideas?

It's the wrong slide stop. The extended slide stop only comes in 45acp you need a 9mm slide stop fitted.

I had the same issue with some cheap mags from Sarco in the .45 1911 I built. I fixed it by bending the lower tab on the followers that engage the slide stop. Fixing the first one took some experimenting but after I figured out the first one fixing the others was easy.

I bent the tab to the side so the follower couldn't move too far side to side or too far to the front and back in the magazine. You don't want to take all the play side to side and front to back out because the follower will bind if you do but you want to take enough play out that the follower can't jump around the slide stop.

If you have a .45 slide stop in a 9mm gun it probably won't help but if you have an in spec 9mm slide stop and it keeps doing it, tweaking that tab will fix it.