Damdam

Hows your humidity? I'm not too clued up on growing indoors but that could be light burn, judging by the pic the left side is slightly brighter than the right so perhaps you catching a hotspot - otherwise if its not light burn and you certain you been watering properly next thing is to check your PH to make sure you not dealing with nutrient lockout

If PH is fine then its most likely beginning of a nutrient deficiency but just looking at it im guessing its wilting from excessive heat/humidity - Raise your lights and see how that helps otherwise consult the link below & diagnose for yourself, bottom half is fine so that makes it easier to shortlist the issue

https://sites.google.com/site/autofloweculture/home/deficiencies-and-excess-nutrients-charts

Good luck, let us know what happens

you let them go dry? First impression, to wet.. but i need a clear!! picture of a few of the leaves. Those with brown spots... if it is what i see. Plus medium you grow and what and how much you give nutes. Looks serious.. dont let that slack.