I strongly recommend just hitting the "Easy" switch and send the gun (and all of your magazines) to the Mothership in Georgia for them to examine; they'll probably do that on their dime shipping-wise, and will thoroughly go through the gun, ideally eliminating any potential or actual causal factors. THEN you can expend a thousand or so rounds.
I like my Gen 3, and it's going nowhere, but I think the Gen5s are an improvement in terms of both performance and ergonomics.
Best, Jon
Sponsored by Check-Mate Industries and BH Spring Solutions
Certified Glock Armorer
Strangely I have recently had similar stoppages with two of my Gen 5 G17s, none so far with the gen 5 G21 but only about 200 rounds through the G21. Never a stoppage through my Gen 4 G21.
My G17 stoppages were about half way through the fully loaded Glock mags.........call me confused
Edited to add: My S&W revolvers don't suffer from stoppages of any kind
And thus Glock has become the 1911....
I see that the Speer Lawman 230gr ammo is advertised as 830 FPS, which is a bit less than their duty load at 890 FPS. I wonder if the somewhat weaker Lawman load could've contributed to the stoppages. American Eagle is listed at 890fps.
Try this:
Unload the gun - bring it up in your firing position and press hard with your grip and look at where your index finger is in relation to the frame - is it close to the slide release?
Now loosen your grip a bit and see if the gun can move around so your index finger gets close enough to brush the slide release.
Here is my hypothesis:
Later in your shooting sessions your grip is relaxing a bit due to fatigue. It becomes acute as you get towards the bottom of a full magazine. The ambi slide release on the Gen5 now can be bumped, causing a very slight drag on the slide. That drag slows the slide just enough to disrupt the feeding process.
If you find you're able to drag the ambi slide release. I would buy a Gen5 slide release and grind the right side (left hand) side down flush with the frame. Install it and shoot 500 rounds, I bet it doesn't happen again.
I'd be willing to place a small wager that the solution is your grip and not the gun. Or rather a combination of the two, you never noticed it with previous G21s, because they don't have ambi slide releases.
That would make sense. Handling my G21 Gen 5, it's hard to imagine my finger touching the slide stop enough to push it up against the slide, but I suppose it is possible given the position of my finger. Maybe I should try a vetting process where I don't shoot more than 250 rounds at a time.