unless you can see definite damge to the slide catch, it basically has to be a magazine issue. definitely mark them and try to isolate the mag. hopefully it's just one. but even if it happens with all of them...
what could be happening is there is dirt or stuff in the mag that won't let the spring push the plate all the way up, which is what locks the slide back. try taking your mags apart and cleaning them well. even though the gun is basically new, there could be old grease or something causing the offense.
a test would be to remove the slide and insert an empty mag. if the slide catch goes up, good. if not, it's either the mag plate not coming all the way up or the catch has been bent somehow and doesn't engage the mag plate fully. both of which you would be able to see better with the slide off.
as far as mag storage rotation etc... everybody has their theory and everybody's theory can be proved right and wrong yadayadayada.
that being said, springs are supposed to only be working ie...deteriorating when they're being cycled. as in loaded and unloaded. so leave your mags fully loaded all the time right? well, springs can sag if left under tension all the time. so rotate your mags right?
my thought is that it is probably not necessary to rortate your mags, but it won't hurt anything to rotate your mags either. i just wouldn't go so far as to mark it on my calendar.
do i rotate my mags? yes, but only because they all function and i don't pay attention to the one that gets loaded for carry after a range session.
