so what you're looking for is fouled out plug in that cyl the code says is missing, the tip that's inside the engine. can only see that on the clean plug in the pic above and it looks good. the other one looks like black oil or something on the threads, but that's usually from outside the engine, like a valve cover leak or something. usually doesn't effects it. but for those pics to be helpful you'd need to know which one came from the cylinder that was missing last time.
I do wonder what you're using on the threads, you said grease but I just guessed you were calling anti-seize greese. but they are 2 different things. now that I see the little black packet under the plug, it makes me wonder if it's not actually axle grease? you can put a thin layer of anti-seize on the threads but probably not good to use grease. to be fair I don't know a good reason why not, other than it's just not done and may make a bad connection to the block electricity thur the threads. these days NGK recommends installing their plugs dry threads. better electrical conductive and the plug needs to ground thru the threads to the engine block for the plug to fire.
with all that said, you'd need to go remove the plug from the car, take a pic of the end of the plug that's in the engine. that would hopefully give an idea of what's going on in there. then if it's not really obvious what's wrong, swap it to another cylinder and then see if the miss fire fault code follows it to that new cylinder.
side note, did you use Bosch plugs last time? I personally have horrible luck with Bosch. these engines seem to run best with the oem acdelco plugs. but not bought from Amazon or ebay. believe it or not there's cheap knock off plugs all over those sites that looks perfect but can cause more issues than they solve. a local auto parts store or a site like rock. auto is usually recommended around here.
does this engine have afm active? #7 is an afm cylinder. is there's a tapping noise while running?
