I sent it back to SIG and the note upon return says:
"We replaced the gas return o rings and ran 2 clips (60 rnds) through it and had no malfunctions. " - Sig
Sig apparently came to the same conclusion that others did in your other thread hijack: undergassed/short stroking.
Then you quote this:
"The rate at which the bolt carrier assembly recoils rearward can have an effect on reliable extraction and ejection, even if extractor and ejector dimensions and springs are absolutely correct. The period of time during which the bolt is behind the stack of rounds in the magazine, neither traveling rearward or forward, has an effect on reliability in that the magazine may not have enough time to push the next round into place before the bolt comes forward again,
Which describes overgassing.
It's one or the other.
God gave you a soul.
Your parents, a body.
Your country, a rifle.
Keep all of them clean.