Ok 1K, took these pics from last Sunday, I already know what part of my problem is, too many guns, too little time. A weekend comes, wake up early 7 30 AM (even though I don't want to and yes that is early for me same time I wake up to go to work would rather sleep in till 10 or 11AM ) drive a hour to the range after 5 or 6 hours sleep (because I stay up late) with a bag full of guns attempting to get as much as I can done with too many at once. All the while allowing myself 30 min each gun before moving on to the next.
This is partly why my SIG 226 and Springfield XDM that I am about to post after this message I both bought middle last year I am only now starting to get better with them. Again too many guns, too little time. These are my final targets of the day last Sunday after fiddling around adjusting the sights, and testing different ammo. As you can see like you, I always have two or three shots that go off and I know it's me, not the gun not the ammo, although after you or me making a mistake the next culprit I would blame is ammo. Getting back to trying to cram in too much at the range at once, 9;30 am to 2:30 PM, by the end it is pretty tiring and not conducive to shooting your best by the end. Someone mentioned blaming the sun as a joke, actually my range faces west by 1PM to 3PM the sun actually is blaring at me from the front and does matter.
Some mistakes are more known and pronounced, others can be subtle but the target shows either. Holding the gun up for a extended time, concentrating on front sight focus, correct grip, correct breathing, correct trigger squeezing it takes physical and mental endurance. I personally get to go out shooting once or twice a month bringing a bag of guns, I know I need to bring less and shoot more of the same gun.
Getting to the Glock, I like my XDM 5.25 a lot better than a stock Glock, for target shooting, feels better, and I have really become a fan of the glow fiber optic front sight with a black rear. Indoors or outdoors with sun in my face or not glow dot is easy to focus on. As time goes by I have become less of a fan of three dot sights. But the trigger on a Glock or the XDM needs getting use to, in the end I do prefer a lighter single action trigger. My opinion the Glock is a top combat or defense gun, but stock without mods not the greatest bulls eye shooter.
I can't diagnosis your problem , but based on my mistakes getting flyers away from a good group, just giving input and I would lean toward the gun not being the problem and more toward human error or the ammo. At 10 yards if I can keep most in the 10 with a couple in the 9 ring I'm happy but usually a couple go in the 8 ring or worse lol.