could be fungus gnats as usually follows coco - which will cause some issues with roots and could explain why development is skewed a bit.
next time you do this - add SNS 203 to the mix regardless. in the meantime get some yellow stickies to see if you have invaders - put the thing right at soil level on a Popsicle stick or pen...etc
now as you've used both coco and soil - you'll have to treat things as soil so keep your pH between 6.5 to 7.5 instead of 5.8 to 6.2.
add a little bit of sugar to your water if is a living soil (1tbsp of raw sugar or maple syrup per 5 gallon RO water)
make sure your water is good and clean - anything with counts over 200ppm will require a RO & Carbon Filter if in City and Chloramine and Fluoride are dissolved. both kill micro-organisms. Sodium locks out everything as Sodium is taken in first before other nutes - which is why anything over 200 needs filtered.
make sure to bring on CalMag if using RO, LEDs and Coco... about 10mL each so if you're using RO water, LEDs for lights and near 50% coco - you'll need ~30mL per 5 Gallons of RO water. always add CalMag before adding other nutes.. Autos love CalMag.
and keep your nutes about half of what photos would use (1/4 to 1/3 of what bottle says, work up to 1/2)
Would a nutrient/tea that has bacillus In it kill of any potential fungus gnats?