what is my issue heat or nutrients.

All plant is healthy not overfed colour, so excess of nutes not the answer. Heat could be. Could be rout bound , too small pot for that girl, first signs Could be ph issues, they always come up in 3rd week of flower. Could be just eating hereself, aka a bit too hungry. That leave curl could be to low humidity for high temperature, check vpd charts in weed grows. Very useful