buffer weight issue

[Tex Nomex]

There is about 1/4-3/8" free space from all the way pulled back to locking on the bolt catch when releasing forward.
With the adjustable gas block wide open, it would also not feed reliably.

So we know it's not a tube issue, at least.

With a marginal gas system:
Any kind or resistance is bad - rough chamber, dry BCG, new/dry rings, mag spring too stiff (new mags)...
Any kind of gas leak is bad - rough chamber, worn gas rings, loose gas block, misaligned gas block, worn gas tube, bad key seal...

You might have a weak extractor not keeping its grip on the case head when pressured by the compressed mag spring, especially with new mags.

I'd brush the chamber, check my gas key and tube end and shoot it with a non-adjustable gas block with a HUGE hole and some not-new magazines next. Sometimes these issues work themselves out after some shooting.