That's a normal wear pattern, but sounds like it's extremely accelerated for some bizarre reason. The magazine puts upward pressure on the carrier, so that causes wear in the upper receiver, where the upper rails on the carrier contact it. That's why you see it only for that short distance, because once the carrier clears the magazine it just kind of floats in space, not making hard contact with the receiver walls.
That is eventually what kills upper receivers, but it normally takes several hundred thousand rounds.
Can't even begin to explain why that carrier would be doing that, though. I don't see anything radically different about it in that area that would cause that. The only thing I can think of is that the receiver wasn't anodized properly. Once that anodizing is gone it will start wearing really fast.
I just don't know, you got a real headscratcher there. What's really strange is it looks like you've got accelerated wear on the carrier itself. Looks to be nitride, and it should take at least several hundred rounds to raise those shiny spots, if not several thousand. Even if it's phosphate, should still take hundreds. Unless you got your grease mixed up with your lapping compound I really don't have a very good suggestion for you.