I had this exact issue shortly after buying my AR. Turns out it was a loose front gas block that began to inch forward after a few shots, causing misalignment between the hole in the barrel and gas block, hence restricted/no gas flow, short cycle, would eject but not feed.
I too have an A2 front sight held in place with two measly set screws, which by far is the most inane mechanical attachment conceived for this part of the firearm, and don't gimme any "need to adjust front windage" excuse. Of course this was my first AR and I didn't know any better. I don't really want to dimple my barrel, and I don't want to clean up a Loctite mess anytime I need to move the front sight. White Oak cuts big notches in their barrel for front sight attachment and windage adjustment, but those are bull barrels, not a NATO profile like I have. My 20" barrel does not have the notches for the pins either.
To make matters worse I live in MA so my compensator has been firmly attached; safe, blemish-free disassembly to fix this is likely going to involve a machine shop and possibly the demise of my current compensator.
Until I decide to tear this apart to fix this, I have resorted to installing a $5 black oxide two-piece machined steel collar around the barrel, directly ahead of the front sight and pushed against the sight tightly. The collar has two hex cap screws, clamps down ultra hard and will not budge, hence the sight doesn't either. Problem solved and the rifle cycles perfectly. It was a cheap fix but outside of a layman anyone who sees it will say "wtf?" Actually it doesn't look that bad. A permanent fix will be done sometime in the future.
Sorry to hijack, but I had the same issue and it vexed me to understand why the front sight was installed so poorly. To be fair the rifle builder did offer to help fix it.