Since this is mag problem (if the 10 rounder feeds fine), there is always the option of replacing the mag with a working unit, but not knowing how available mags are in your part of the world, it may be easier to just correct the one on hand.
If you take a look at this photo you posted, you will see the receiver mar’g just below the feed ramp in the upper receiver it’s self. This mar’g is being caused by the bullet low feeds out of the mag (bullet tip striking the upper receive and not the feed ramps).
Breaking in, cleaning up the mag.
First were going to start with setting the spring, and mate the follower to the body.
To do this, you take a ruler and push the mag follower all the way down, then let the mag snap back up on it own. Do this about 20 times.
Since you have stated that you have already pulled the mag apart to clean it, stripping it down one more time should be a snap.
With just the mag body in your hand, run your fingernail down the under side of the feed lips to feel for burs.
Check the very front of the mag where the tip of the bullet tracks up the inner side front of the body.
Check the upper guide section of the mag for burs (it’s the section just behind the shoulder of the round of the photo that I posted, and the one with the bottom edge bur sticking out and waving at me).
The short version is if any areas that I listed above have stamping burs, they should be removed (stoned) so that the contact edges of the mag to the round should guide the round, and not scrap the hell out of it.
Once you have the body corrected, look at the mag follower. If you find the bottom of the skirt is littered with casting edges, us a razor knife and address the edges.
Follow this up by cleaning all the parts and reassembling the magazine.
Now before re-installing the mag into the rifle, check the mag release button to confirm that the thread section of the mag release (inner part) is flush with the button it’s self. If needed, you press all the way in on the button (use the back end of a pencil), and reach over to the other side to give the catch another spin if needed. If you find that the catch only needs to be spun ½” turn to flush the threaded section, them you will need to spin the catch all the way out, remove the button and re-orient/spin it 180*, then screw the catch back in to flush the tip of the threads out with the button.