I'm not a Glock guy, so I don't have specific instructions to give you, but I see lots and lots and lots of Glocks being shot in practical pistol competitions, and they all drop their mags freely (a gun that won't drop a magazine is non-competitive/useless in USPSA). Try to figure out where it's binding/rubbing and then polish that. Or, if it's just one magazine that does it, throw that mag away or mark it only for certain uses.
But fix it. A magazine needing to be stripped on a gun designed to drop them freely (or dropping sometimes but not others) is a failure mode.