I shot it for the first time today.
With a single round in the mag and it did not hold the bolt back. It will hold manually with empty mag. It will eject the empty round but not pick up the next round most of the time. It did pick up the round a few times but would not fully chamber it.
It could be a magazine issue. I was using unbranded 450 Bushmaster mags from the gun show. All did the same thing. However, they will hand cycle through the whole magazine. I will get some better ones ordered.
I do believe it is likely a gas issue. It could also be the buffer. I am using an H1 buffer. I can't get my video to load where I am.