Something VERY odd there if two mags for the same rifle won't lock in, but the factory stock one that came with it works fine. Dumb question - you are absolutely sure they are the same mags?
As for the trigger, I would simply adjust the regular and set trigger to your preference. Mine was just right from the get go, but I have known many people to take advantage of the adjustable trigger. if that doesn't work, then definitely get a hold of CZ-USA, 1-800-955-4486. i would call them anyway about that oddball magazine issue, sounds like the spare mags are wrong, not the rifle.