Update: went to the range with just the 8" upper with new replacement bolt.
Ran like a top, 200 rounds and change, not a single hang-up or issue, bolt locked open. 115-gr factory Blazer Brass, and 147-gr subsonic through an Omega 9K suppressor. H1 buffer. Fast strings of doubles and triples, even some tac reloads which would be the death knell before. Ejection was a consistent and healthy 4:00-4:30.
So it would seem (again only 200-250 rds) that the chipped bolt lugs were the issue (again only with the shorter 8" upper but not the long 16"?), but I can't help but wonder if like before it's fine n the beginning but will soon just all go to hell. I'm still pretty confident in my longer upper getting through a match as it has each time, but the shorter one for 'fun' matches and maybe even some home defense with suppressor...still wary. Can only tell if it's really fixed if it holds together up to 1000 rounds or so. Last round count where it went bad after refreshing the extractor and ejector springs was only around 450.
Will see if CMMG will still offer some sort of replacement for the damaged bolt.
At least from the looks of out (again only first 200+ rounds), the lugs/edges seems to be fine but you can see wear the brunt of the contact wear is. Except the second and third lug after the extractor seem to have their leading edges at an angle compared to the rest. Don't know if that's from initial wear or by design.