I have a plant doing that right now, too. For the life of me, I cannot fully figure out why, but, both yours and mine look healthy enough so I say just keep pushing.
My best guesses: "wet feet" or keeping the roots wetter than they'd like, BUT, i stopped watering mine for 2 days & it still showed leaf-edge curl. I also thought light intensity but it's the furthest from the light.
Could just be a sensitive pheno/strain.
OH ALSO, my humidity in my tent is really low, how is yours? --i wonder if this is just a symptom of lower RH than the plant would like