The plant that stays in the center is having some ...

I don't want to scare you but I think it has root problem.two things coming to mind when you say sugar leaves are curling down,gettin yellower and crispy ; bud rot or root rot problem. you might be overwatering it for a while or if you think you havent been overwatering this is because it is right in the middle and can't get enough air to soil surface to help it dry faster,it may be too humid in that pot. yours are still small flowers that's why I don't think bud rot is an issue but you definitely should check that pot closely.Lack of nitrogen doesn't appear like this,firstly lower and bigger fan leaves get yellow in that case.I wouldn't water it for a week to see if it stops spreading.and providing extra air or space to that pot would be a great idea.I know you wont be able to move pots because of scrog but you can defoliate neighboor plants' leaves. your weekly review section is a joy to read btw.I like how you analysed them each and separated into phenos.I have that midnight purple pheno you were talking about,smoking right now.recently harvested,check out my diary if interested.good luck everything looks cool.