Sounds like it might have a bit more protrusion into the mag contact point than it needs. Either too much material left when it was machined or a burr or something.

Have you removed it so you can examine it closely. I believe it comes out pretty much like a glock. A little rod just needs to be flipped out of the notch and the release will push out. A person could even stone or file off just a bit and test fit now and then. Being careful of course to make sure you still have a good positive connection so the mag don't go walk about.

Some have added a little dab of material on the button so you have more to push on eliminating the need for the thumbnail trick. That might solve your issue as well.

Wish I was Greg, I'd post some pictures of that area but I don't have that natural talent.