Remembering my old Buckmark, sometimes the mag release spring can get slightly out-of-position, and then the mag release won't work correctly. Take off the right-side grip, and see if the slightly-curved flat spring is in the little frame cutout where it belongs. If not, return it to the correct location, and carefully reinstall the grips (making sure the spring doesn't move).
I remember this spring getting out-of-place almost every time I pulled the grips off my Buckmark for cleaning; I've heard other folks complain about it too, so I think it's fairly common.
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)