Take it out and fit it to all your mags outside the rifle, check the teet protrusion into each mag, note any different dimensions and mark mags accordingly. I do not recommend it, but I customize my spring guide tips for quicker reloads at three gun matches. I have also had to customize different mags in the hole area and the back saddle at the top. I take off 1/8" of the very back at the top, around the U shape....makes for super fluid reloads.
Another place to check is the mag catch spring tension or wear of the top of it. Also check all mags for same location of locking tab welded on the back. Measure from the bottom of the mag to the bottom of lock tab, then the top of mag to bottom of tab, you will find your problem mags this way.