My mag release has the exact same play with a mag in and no play with the mag removed. My mags function great, going in and dropping out.
For me it's more of a curiosity issue, because it didn't do it when it was new but it does now.
It doesn't cause me any problems whatsoever in terms of function, but I was curious enough to call Ruger a couple days ago. The rep basically told me to look at item no's 55 & 39 in the manual and that it's normal for there to be play because of something to do with how the spring reacts when under pressure.
Not entirely sure I buy the "normal" though, since a lot of other SR9c owners don't seem to have this occur. (maybe theirs isn't normal..., as mine apparently wasn't the first month or so I had it???)
I got the impression that so long as the mag functions normally they were uninterested, but if there was an issue with inserting or removing the mag then it'd be worthy of a look-see.