[fastbolt]

The chatter marks like those pictured typically happen in the subcompacts when someone fails to fully seat the rear of the recoil spring assembly completely into the barrel lug's semi-circular "half-moon" notch for reassembly.

When it's not fully seated in the circular notch, and the slide & barrel are put back on the frame, the rear edge (metal) of the RSA is out of position and can dig into the frame as the slide is retracted for installation. This is typically an owner/user caused error. (In the full-size & compact Gen3 & earlier models, failure to fully seat the rear of the RSA's rod fully inside the notch can result in unwanted pressure being exerted on the plastic rod's base, and the base [rear] can be snapped off.)

When the slide & barrel are removed during field-stripping, the rear of the rod will be sticking down a little bit, looking like it's sort of "hanging" off the notch, and that's normal, but it must be fully seated back in the notch for reassembly (and the rod should be centered and parallel with the barrel, as well).

Mostly when this sort of damage occurs to a frame from failing to properly seat the rod during reassembly, it's usually cosmetic (although it looks nasty). However, having your particular pistol examined in person by a local Glock armorer would allow him/her to inspect the frame and make sure it's only cosmetic damage and that nothing else has been going on.