Check your magazines again. The original non-drop free mags and the first generation drop free style did not have a metal lining all the way up to the top of the lip. After some use, the top front of these mags starts to peen outward, allowing the nose of the top bullet or front of the follower to ride higher than it should. This can cause all kinds of malfunction problems; mostly usually the slide locking opened after every shot with a still loaded mag. Glock corrected the problem when they introduced the guns with finger-grooves and rails, by running the metal lining all the way up to the top front edge of the mag lip. Since your gun doesn't have the rails, it's safe to assume you have the older style mags. Check to see if the front edge is beginning to roll outward. My 35-officer agency has issued the Glock 22 since Dec 1990, and aside from some ammo problems early on (that I addressed on another post); most other malfunctions have been atributed to these mags.
Safe shooting,
Mark Garrity
Safe shooting,
Mark Garrity