I'm somewhat at a loss since I can't put hands on it, at times I lean to something not right in the chamber and yet at times it chambers which seems the chamber is OK and maybe carrier group related issues.
If you have a 308 snap cap or dummy round, I think I'd try removing the trigger module (the lower) and cycle the snap cap. With the trigger module off you should be able to see the carrier cycle and maybe see if something in the bolt or receiver rails are hanging up. This should also eliminate mag or trigger module/bolt catch induced malfunction I would think.
Other than that maybe a complete detailed cleaning of all the action parts and a serious cleaning of the chamber and locking lugs with a chamber brush and good cleaning fluid ( not just some CLP)
I'd really inspect the cam pin and cam pin path for any odd marks or crud, the surfaces of the bolt and bolt body and if nothing stands out lube everything well with a quality lube.
Pull the gas system and inspect the gas plug/regulator and piston.
If still the problem persists it might be time to have FN inspect it, unless someone else has some better useful recommendations.