It looks to me that you don't have a clean hole.
( sorry for getting personal ).
I'm not saying that is the cause of the malfunction , but could be a part of it.
It looks to me like the bolt face ejector hole was drilled with a dull bit. The burr on the
hole is leaving the marks, like it is trying to cut a hole in your brass. Not just squishing it into the hole.
Are they sending a bolt also?
I'm not up to speed on diagnosing an over gassing issue, but I don't think that the under-par bolt is the only issue.
I hope bushy gets you taken care of, and you don't get discouraged because this is a really cool caliber.
It's customary that gun companies send extra mags when they have to do warranty work.
( would be kinda like sending extra homework in this case )
Maybe they could just exchange you an upper with one they have in stock after giving it an extra peek.
That would save you from having to wait on two trips plus time.
I feel that you have put in more than your share on solving it.
Tell them I said " Just give him the pickle!"
Trying to think if I can come up with something else helpful.