Im not positive but my guess is the plants is preparing for a big surge. I found so far (1 grow, repotting) that the smallest plants hieght wise have the bigger root systems. I have a pair of northern lights females right now, the small bushy one had roots starting to turn in a 1.5gallon pale after 28 days while the taller (twice as tall) one had DICK for roots upon transplant. I understand that autos dont get big to begin with. I have 9 1in blueberry low sprouts right now on day 3 I wanna say, just starting there first set of reel leaves. I personally wouldnt worry about it if you start them in the pot theyll finish in.