After several frustrating range trips I hope I have solved my issues with the 6.8. An A5 H2 and lots of AGP adjusting finally got the bolt to hold on last round both with and without suppressor. But the fired case would not eject. I had to pry each one off the bolt face manually. Much research indicated several possible causes - debris under the extractor; defective extractor claw, machining defect on bolt face, weak extractor spring, and under-gassed.

The last I pretty much unscientifically discounted from the get go. Even with mid-gas this has more recoil and gas in the face than my canned blowback 9mm and .308 ARs. And I trust ARP got the gas port right.
The claw and bolt face were pristine and zero chunks in with the extractor. Today I replaced the spring with the Sprinco recommended 4 coil which fetlt stiffer than the stock ARP. So that may be the cure. I did find a machining defect in the extractor pin hole. Unlike every other bolt I have torn down this was like trying to knock a bolt catch pin out. Major pounding. One hole side had a ridge halfway inside that reduced the inside diameter. Not wanting to risk opening the hole too much I just reamed with a square file handle until the pin went in still tight, but with less binding. Though I doubt that would restrict extractor movement. But possible.

Manually pulling the charging handle now pops the round out which it did not before so fingers crossed. Range time next week weather permitting.