If the round is extracting and ejecting properly, and it's stripping the next round from the mag into the chamber, it isn't a gas issue.

If the trigger is failing to reset, AND the rifle isn't doubling when you release the trigger after a shot, AND it's ejecting and stripping the next round into the chamber:

1) Disconnector isn't catching the hammer. This would mean the trigger would simply be dead as if the rifle had been dry fired, because the hammer would follow the carrier back as it closed. The fact you need to half cock the charging handle is one troubleshooting clue for this. HOWEVER, whacking the rifle on the side would do absolutely nothing, so I'm doubtful this is the issue.

2) Disconnector isn't RELEASING the hammer to the trigger/sear. You SHOULD hear a distinctive "cluck" sound releasing the trigger after a shot, where the disconnector releases the hammer to the trigger/sear. If the disconnector isn't traveling freely or is over-length, it won't release. Sometimes a sharp "whack" to the side of the rifle would cause the disconnector to slip from the hammer, just as half cycling the action might cause enough jarring to release the hammer.

If the gas key were lose or gas tube misaligned, causing the carrier and bolt to fail to close into battery BUT allowing sufficient travel for ejection and reloading, the trigger would not be dead, as the hammer is cocked WAY earlier than cartridge ejection. The trigger would be live, the carrier would be visibly out of battery, and attempting to fire would drop the hammer on a "squishy carrier" or stuck carrier, where it wouldn't hit hard enough to ignite (it MIGHT fire), but would offer an audible hammer fall - dry fire click. The hammer can often jar the carrier/bolt the rest of the way into battery, forcing over a partial misalignment. Magazine feed lip drag would cause the same result - which isn't consistent with what you're describing.

Sounds like you simply have a tolerance stacking issue in the fire control group, and your disconnector is failing to release. Couple options there - replacing the disconnector the best of any option. Stoning a bit off of the disconnector to shorten it's claw is a second option. Peening the front tip of the disconnector, or adding a dawb of devcon steel under the tip to help the trigger push the disconnector off are a third option (1 & 2 are orders of magnitude better).