Norinco Olypia is fun fun fun

[marshall]

If the slide is not releasing with a new mag, it may be going in too far, and slide hitting back of the mag, or if last round is real tight, could just be too hard to strip off
Try pulling the mag down against the lock, base may let it ride too high, with the slide closed ,the mag spring ammo pushes it down on the lock? mag release.

I had some old mags for a couple pistols with weak springs , and they would not always have enough power to push the slide lock up when mag was empty.
Hold the slide back with your hand and insert empty mag and see how the hold open works , it should stay up when mag is removed.
Just a shot in the dark as I have not worked on this model.

 

[alpining]

... One oddity, if you insert the mag with the slide locked back, the slide hangs up and will not move forward to chamber a round. On the last round when the slide locks back, when you remove the mag the slide moves forward instead of staying locked back....

Did you have these issues with the factory magazines too, or just the TripleK ones?

Can you manually release the slide stop when the slide hang up happens?

Coupled with the second issue, it sounds like a magazine fitment issue. As marshall said, if you play around with empty magazines and watch the slide stop actuation you might be able to diagnose the cause.