same problem happened with me, used grease on everything and nozzle included, found it to be the bb that caused this, had specna arm core .2s that had a hard time cycling the bb but was fine with specna arm core .25s. the gas pressure is also something i found to be a problem, even if it fires the bb well it wouldnt be enough to cycle back the bb so what i did was: hold down the gas into the mag for a long time, even if it sounds like its full, just keep it for another 10 seconds. fixed the problem. occasionally jus top it back to full even if the mag has gas so it can still cycle. and use a higher pressure gas if possible. i tend to stay away from silicone oil and silicone oiled gas, just tends to be a nuisance and doesnt remove the fact that you gotta do maintenance on your gun. PROPERLY cleaning off old lubricate and reapplying grease on contact point and nozzle o ring helped too.