Bought my first glock, interesting experience.....

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Truth

This sounds logical...

Barrel swaps change the fit of the frame and slide in a Glock.
If a barrel tightens that fit (pushes the slide upwards more), there will be less engagement between the striker and the trigger bar tail that holds the striker.
The tail of the trigger bar can be bent upwards to get more engagement with the striker.

[major burnout]

Need a stabilizer brace!

And more than 5 rounds in the mag.

[Bakerloo]

'Interesting experience'. Clearly OP you have a gift for understatement.

'unwanted ammo use' I like that.

Doing my RO shift on the public line we had an similarly 'new to him' AR that experienced 'unwanted ammo use' just last Sunday. It had been the previous owners competition rifle. Likely for shooting 'mouse loads'. After several of us looked at it, we figured out he had shaved the disconnector down to the point where, after three mags of full power 5.56 ammo it got, real exciting, for the new owner.

You just never know with used weapons. Good luck OP.

Way back in '84 I got my 1st AR. A "friend" of mine (who was an ex Army armorer) said he could smooth out the trigger for me. He did and brought it back to me. I took it out to river to give it a test drive. I had 3 thirty round mags loaded up and another couple hundred rounds in the ammo box.

I tossed a can out there to shoot at. First squeeze was about 10 rounds of full auto. The next squeeze emptied the mag. I shot the remaining 2 mags full auto, then got out of there. The next day, I bought a new LPK and returned it to normal. Tossed all the old stuff. Now, it's an old school RAW sitting in the safe.