CCT and R:B ratio don't have that profound of an effect... it won't make normally fat leaves develop as skinny leaves.
This can be caused by overfeeding p or k, but can also be genetics.
It'd be rare, but a Zn-deficency can cause skinny new groth, too, and also coincide with interveinal chlorosis, which unless the grow lights are decieving, looks to be the case here. This would more likely be related to pH rather than an actualy deficiency in zn..
Soil typically has this stuff and soilless should be using a hydro nute line that has all the trace elements included too... so, more often lockout.