Are you not adding any calcium or magnesium?
This looks like an early stage of calcium/magnesium deficiency.
Because ur leaves looks green enough, they don’t lack nitrogen. And phosphorus and potassium is almost not used in VEG stage.
So I would recommend adding some Calmag to your plant! And look over your ph in medium. It can be a ph problem as well.
If ur adding calcium and magnesium already it’s 100% a ph problem!
So if it’s a ph problem, just feed her with ur normal solution you always feed with and flush out the bad ph until you get the ph you want in your runoff!
Good luck my friend 😁