That could be foxtailing and along with top leaves curling says to me the light is too strong/close/intense.
It also looks like it’s possibly starting to re-vegetate. This is usually caused by interrupted darkness. Either by a tent letting light in through a leak or by you looking at them with lights off. It’s ok with automatic plants but not photoperiodic plants.
Maybe also caused by light intensity tho im not certain on that.
You can get apps that measure the light although not dead accurate the PHOTONE APP is probably the best
So best case foxtails, worse case reveg. Either ways best of luck to you