Deficiency/toxicity/virus/bacteria! What could it be?

At fist glance and with my decades of experience, I would say it's a calcium deficit and your best options Make sure your pH is balanced, re-apply a new nutrient mix if necessary. For Coco: Ensure Coco has been buffered with Ca/Mg. Without buffering, Ca and Mg deficiencies are more likely to occur. Organic Solutions: • Egg Shells. When crushed in soil, it will a be a slower release. However, crushed egg shelled, warmed up, mixed with vinegar (1:10) as a foliar spray will be a much quicker way for your plant to recieve calcium • Dolomite Lime • Organical Magic Inorganic Solutions: • CalMag Supplements • Calcium Nitrate