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Could be a lot of things but need some more information. What your style of growing, how much are you feeding them ec/ppm? Is it only happening on the bottom?
So of the bat it looks over fertilization, that clawing of the leaf is the indicator. Also if you have a fan that is blowing hard on that portion of the plants than that can be the issue as well. Too much wind can cause weird damage.
Also just looking at a couple pics they look like they're not getting enough light. I am a fan of lollipopping so I would just cut all that stuff off. If there is not enough light you won't get much bud anyways and the potential of disease is higher in low light spots