Well, I contacted Proof and went back and forth with them showing pictures and videos. Bottom line is that:
"Alright so our engineers here spoke to their engineers, and what they had said is that rifle is optimized around a 308WIN cartridge, so there are a few things that you can do that should help with the feeding issues of the rifle!
What they had said is that their rifle tends to like the lighter 6.5CM rounds over the heavier. Also, if you are handloading they had recommended to load them on the shorter side for better feeding.
Finally, they had said if you run the bolt a little on the fast side it should help with the feeding as well.
I hope that is able to help!"
So the bottom line is that "
optimized around a 308WIN cartridge" basically means it's an un-correctable design flaw. I might yet take my Dremel to it with a felt polishing cone and polishing rouge to remove just a tiny amount of material and slick up the chamfer.