OK, that would indicate it’s more likely an issue with the lugs rather than the cocking mechanism. The male lugs on the bolt do look smooth in your pics. Do you see any rub/galling marks if you look closely? I would be interested to see what the female recesses look like. There must be a burr or some roughness to cause that chatter. I don’t suppose you have access to a bore scope do you?
If it were me, I would scope it and send it back if a problem is evident. Even if it doesn’t affect function, that would drive me nuts and is an obvious QC issue.
If I didn’t want to send it back, I would mix up some Kroil (or other lubricant) and some JB bore paste, brush it in there and all around the lugs, and work that bolt up and down to see if it wears in. Then flush copiously with gun scrubber, or non-chlorinated brake cleaner, and then lightly re lube.