I want to say you are doing a great job. Just relax. I have rescue birds and re-homes and all birds pluck now and then. My TAG was occasionally plucking for attention when he came to me. You have to ignore it. If you have another bird or even another person in the house, you can give them a treat when your TAG plucks. He will learn what the other person/bird is doing is the behavior that gets rewarded, not plucking. Reshaping plucking behavior is hard b/c the biggest thing you can do is nothing. Other things that help a plucking bird from my experience is foraging. I have a minimum of three bowls in each of my birds' cages. They all have a little bit of food in them. I started out by covering them with one piece of newspaper with a hole I stabbed into it with my finger while they watched. It took no time at all and they were ripping the paper. Now I cover each bowl with a thick layer of paper wrapped around it and use the wire rim holder to tuck the paper covered bowl in. Easy! Next, I also put pellets in tiny paper souffle cups - just unstack them and teaspoon in pellets, fold shut, drop in bowl, foraging toys, baskets in cage. Last, all treats go into boxes. I recycle toothpaste boxes and an small footprint box. If the box is too big, I cut it up into fourths and puzzle it back together. The nuts and nutriberries are wrapped in souffle cups and stacked intermittently with newspaper. I put a nutriberry and an almond in each box, run a piece of string through it to make a loop I attach to a quick link I leave in the cage. My birds are very busy and since they are doing so much shredding they don't shred their feathers.
Also be sure to reward all good behavior. I heavily reward my TAG talking. He even says "wanna eat?" at dinner time. Keep up the good work and don't worry about a few feathers. Just keep reinforcing positive behavior.