Went to the range today and shot about 200 rounds. These gouges in the left and right of the slide were not there before today. I didn’t have any misfires or jams. It’s an old Glock 22 gifted to me by my mom. It was her service pistol at Nashville PD when these were new on the scene so likely thousands of rounds and put away wet.

What would have caused this?

Maybe this?

Those wear marks are called "slide peening". They occur when the top of the
locking block contacts the bottom of the slide when firing. Slide peening occurs
primarily and most noticeably on .40 caliber models. It is perfectly normal and
it will wear to a certain amount and then stop. These wear marks will not have
any effect on the gun's reliability or accuracy. If the edges are too sharp you can
smooth them out with a file or stone

https://www.glocktalk.com/threads/glock-22-slide-wear-marks.889066/

It's from the locking block repeatedly rocking up a bit during cycling. It gets to a
certain point and then doesn't get any worse. It was a lot worse in the 2-pin frames,
and is why the third pin was added.

https://www.glocktalk.com/threads/gouged-slide-rail-wtf.1740214/

Hard to tell, but it almost appears like brass deposited onto the slide versus gouges in the slide.