The Magazine release has to fit into the notch on the front of the magazine. This is what locks the mag into the pistol. Maybe the spring on your release is weak or the end of the release is worn? When you insert a mag does the button pop out slightly as the mag gets to its final position? Maybe something is stopping the mag before it gets up far enough for the release to snap in. Can you lock the slide open and push the magazine out once it is inserted? I think with a little examination and experimenting you should be able to find the problem.