Whenever u see this type of yellowing ( progressing from the lower leaves upward)
It's a big red flag for N deficiency. Your plants a simply asking for more. Up the N in your feeding schedule and I'd say there's a very high chance they recover quickly. It's your call but if those were mine, I'd up the N intake (not too much) and go from there. U may think what your giving is enough but always remember, every strain and even pheno within that strain can differ. Example- this batch of seeds wants more cal-mag than the last batch I grew, even tho it's the same strain. I would only speak on things I'm sure about. I'm sure those plants need more nitrogen ESPECIALLY being in coco. coco unlike soil offers no nutritional value to the plant, making it more likely that these types of deficiencies can occur