What is your water/feed schedule? Are you still in veg? How hot is the growing environment? How close is your light to the top of the canopy? At first glance my limited opinion is heat stress above 86*f **edit: looks like you're still in 100% veg so ignore my veg question
I think your right I had this happen to me from it being to hot with poor air circulation so what I did was bought a air purifier about 50 bucks and added a fan to blow towards the light to push the heat away from the girls Sent from my SM-J320R4 using Grasscity Forum mobile app