Are they all 10-round, genuine S&W? As I recall, there were some problems with the 12-round mags fully seating...not an issue here in NYS, where a 12-round mag is illegal....

I would also look at the problem mags for "rub marks" on their bodies in case they have a bulge, and also see if the latching slot is slightly undersized or slightly mis-located...judicious use of a tiny file could correct that problem, but, go very slowly, trying the mag after taking off just a 0.001" or so at a time. A slight "bulge" could be smoothed with a Dremel tool with either a very fine sanding drum, or a Cratex-type abrasive, then, touch-up bluing. If you go that route, cover the sanded area with layout dye or even a felt-tip marker to see if there's still rubbing...