A little more info would help figure out the issue. With more knowledge of the environment including nutrition, soil, ph, ppm, temps and humidity we are just tossing possibilities out. I look at the plant and without more info I think two issues, light stress and zinc deficiency. But again that's a poke in the wind. If you can't get things like ph/ppm intake and of medium I'd suggest flushing, restart the nutrients more balanced and raise the light a little.