Looks to me like drowning plants. are you using a bubbler or just that drip line? and 5.8 is ok for DWC though 5.5 is usually what I shoot for, but 210 ppm? if they are already rooted thats a bit low, imo you need to add a big time bubbler to your res and use more nitrogen,
I usually dont see stuff like that in my clones so I cant really comment on the underdeveloped roots, however IMO you will see better results if you ditch that drip line and raise the res water to just touching the roots and throw in a bubbler