I have a pair of Gen 4 Glock 19 Summer Special Editions with front slide serrations, night sights, etc... I've been having an issue with with the slide locking back while firing randomly. Just to fire off a few points, the first time this issue popped up, I turned it into a local armorer for a look over and we all came to the conclusion that I wasn't used to the extended thumb release on and was manually locking the slide while firing. I didn't change anything out and figured I would just working on my positioning and training to learn the new system. Over time I found the slide lock was not the issue. I actually have no idea what could be causing it at this point, except maybe frame flexing while firing. The slide lock is not engaged in anyway shape or form when this happens. Depressing it does not release the slide and it's not raised enough to depress anyways. It's not a feeding issue as the round isn't engaged by the slide yet. It doesn't appear to be a magazine issue, I've cycled dozens of random mags through it and used them in other platforms. The issue is limited to the G19 SS. I also had one of the locking pins work itself out of the frame on my last range session. I ran through about 200 rounds, started breaking it down when I got back to the house and found the pin a third of the way out. Here's the kicker, this effects both of the G19 SS's I picked up. I ended up selling one of them and come to find out the other one has had similar issues with similar results from trying to figure it out. There's no warranty option at this point and that's my fault as I drug my feet on this. I was really convinced it was me and not the weapon, but it didn't materialize that way. Between that moving into a very high overtime position, I just never pursued the factory warranty option like I should've. Both weapons are relatively new as far as I'm concerned. I have less than 5k rounds on mine for sure, probably around 2k to be honest. The other one has less than 2k rounds. I'm not new to Glock platforms at all. I've carried them for years and have over 30k rounds on a stock gen 3 17 I used for competitions. I would love to figure this out and keep these in action. It happens just infrequently enough that armorers haven't replicated the problem yet and they haven't been able to find anything either. Otherwise, I'm just about ready to move on to a compact Sig. I don't carry for work anymore, but I still don't want to deal with this in a carry gun.