i having the same issue. thought i had all my bases covered, ppm,ph, nutes, air flow, temps, light seclusion...blah,blah blah but getting same results you are.
i am trying to reduce watering to promote or force root growth/stretch. (not plant stretch)
also added a bucket of water to the area to evaporate and increase humidity.
tough to say since we are both in same situation and plants are so young.