Carbine gassed guns are the only ones that need extra power extractor springs, in fact a rubber o-ring added to a mid- length can cause issues. They all need a good extractor.
I had one with the same issues described in the OP. Removed the O-ring from the extractor spring, and no more issues. Nothing wrong with the BCG; the stiffer extractor spring was shaving brass on closing bad enough that a stray sliver of brass would prevent lockup occasionally.
My experience is that a correctly tuned gas system of any length doesn't need an O-ring. That means making sure it's not over-gassed of course.
