I got a new SVI Single Stack 45 last year and had similar problems. It took me awhile to figure out, but it sounds like you may have a similar problem. I think you may have two issues actually. My gun would not work with Tripp 45 mags which was all I had. They ran fine in my STI Sentry. I could not insert them far enough to get the mag catch to hold them. I tried Dawson's mag catches for lowering the mag etc., but that wasn't the problem.
The left side "lip" of the magazine (at least on a Tripp mag) would push the slide stop upward. I ruined a slide stop trying to remove material from it to get it so seat Tripp mags but also lock the slide back on empty (where the slide stop is raised by the mag follower after the last round is fired). After a new slide stop, I finally just took a Dremel tool with a sanding disk and ground about 2mm or so off the left side of the mag at the top where it would contact the slide stop. The mag tube, not the follower. You might take the spring and follower out of the mag tube then put the basepad on, next hold the slide back to here the slide stop is lined up with the slide stop notch (in the slide) but push down on the slide stop so it is at its lowest position, now gently insert the mag and watch the slide stop, if it is pushed upward into the notch, you need to file on your mags (or the slide stop). The mag tube is pushing up on you slide stop which is why you can't drop the slide with a mag in it. It will not effect the function of the mags. They ran fine in my Sentry before and still do.
I think you other problem is probably related to the ejector as others have discussed above.
I am no expert, but it is just something to try. They are fantastic guns, but I believe the tolerances are very tight which occasionally creates other weird issues.