I would be certain you are consistent in your training, because you are with your dog 24/7 not the trainer.
#1 CGC shouldn't be a goal with a very young pup..AKC STAR would be a better beginning. Personally I don't think dogs under a year should be given a CGC certificate.
#2 A one hour class for a young pup is way too long, unless you are changing up what you are working on and a young pup cannot absorb enough when you change it up like that!
#3 repeating/proofing is part of training, even what the dog learned 2 years ago, you refresh and keep on with consistency.
#4 I'd rather have a distraction while training, when you go out in the big world if your dog doesn't have this to work through, you'll lose him right off. Training through distractions is wonderful....you need to keep the focus on you and not the dogs/people that are in the surroundings.
#5 keep on training, six weeks is nothing in a dogs(pups) life....they are forever learning.
I feel the he performs his commands because he feels that he has to, not because he wants to.
are you engaging him? Enthusiasm comes from you and you bring out the excitement to train, boring will keep a dog flat and it will check out.
Maybe try using a ball or tug mixed with the treats for rewards, I bet you'll see a different dog! Good luck!!