Possibly a defective cartridge. I’ve seen a factory cartridge that had the case folded over as the bullet was seated. Like this:
View attachment 83094
(Picture from the web)
We used to see that when I was shooting a lot of handgun. Usually WWB. I wouldn't call it 'common', but it did happen. Out of a group of around 30 guys who shot weekly for many years, the large majority shot Glocks, all calibers and many different models, shooting reloads with many different powder/bullet loads, and a lot of lead bullets. VERY rarely did anyone experience a malfunction, and I don't think any of us cleaned them or did any kind of maintenance. A lot of guys tried other guns at first and almost all ended up getting Glocks. I started with a Kimber Custom II. I got really good at mag changes and malfunction drills with that POS, and that is what drove me to Glock and haven't looked back. XDs were coming around then, a few guys shot them and they did ok.
A buddy shot his 1911 there for awhile and reluctantly broke down and bought a G17. First day he showed up with it he was still on the fence about it. We all gave him a couple rounds of whatever we were shooting that day, and he loaded his magazines randomly from 'the pile'. It was comical because of the differences in the report, recoil, etc but he did well in the stage and never had a malfunction.
I had a case head separation with factory reloads once in my G17 Gen2, I got a face full of gas, and it blew the mag out the bottom of the gun. Fields stripped the gun, found nothing wrong, put that magazine back in the gun and finished shooting it.
I find a lot of guys who say they don't like Glocks aren't basing it on real world experience but on anecdotal second hand info, and when I drill down with them they really can't explain or support their position and that is totally fine. Glock grips over all suck in my opinion but I have learned to shoot them and have gotten used to them, I have smaller hands and the G48 is the best fitting stock Glock grip for me by far. Given their performance, versatility, simplicity, ease of maintenance, and cost they are a tough platform to beat