What are your temps and humidity? Sometimes the leaf curling up is a heat issue, or too dry, or both.
If that is all in range, it could be continuing signs of overfeeding. Third, it could also be the lights are too close! Or a little bit of all three even, as I have had this issue myself.
As close as you are to finishing, it is best to resolve this problem because one time I had this around the same phase you are at, I did not fix it and my yield suffered greatly because they could not finish to full term.
From looking at your comments in this thread, my first guess is overfeeding.
Those are the three main culprits for tips curling up however, at least in my experience.