Slide lock not working?

I just finally got my hands on an SA-35, my first ever experience with the High Power genre. I’m pleasantly surprised at how excellent the trigger is. But, all is not well.

Frequently the slide will not lock back on an empty magazine. The slide lock appears to be sticking and often needs a bit of help from a well-placed thumb pressing up on it. Once that’s done, it works just fine.

I locked the slide back with the safety (in the takedown notch) and then worked the slide stop up and down a hundred times or so in an effort to free it up some, and that has appeared to help somewhat as now the slide locks back on its own 50% of the time. The slide lock is just barely engaged when it does work, and inserting a loaded magazine would probably be enough to cause it to fail and let the slide go forward by itself, thereby chambering a round.

I‘ve never heard of anybody else having this problem. I haven’t fired it yet so it’s possible the violence of actual cycling will be enough to let it work the way it’s supposed to. But if not, does anybody have any advice apart from sending it back to the mother ship?

I should add that it’s extremely difficult to remove the slide lock during field stripping. It’s super-tight in there, which I suspect is what is preventing it from rotating on its axis when pressed upwards by the magazine follower…..