Looks great dude. could be a number of things from stunted genetics to nut burn early. just proceed as usual. Just continue. Like kids in families. you can get weak smaller in the same batch. if its one. It can pull out of it and be fine. Over time you will find weaker looking plants in a same run produce the same weak results. Unless something directly effects that one. The leave structure looks super and the definition on the leaves tell me they are very healthy. I luv purple in a plant veins but that's just me. Heck I am experimenting with a new nut combo that makes veins yellow and they look superb.