Dont know if i hit the right category but could yo...

Hey there, so first i thought about calcium deficiency because of the color and where it's located(where light is hitting that leaf) and phosphorus deficiency can do odd things like this also, but your nutrient line up looks pretty solid. Perhaps raise your ph just a couple points? Maybe that might be locking a few things out. Unfortunately with nutrients they're all available best at different ph's like calcium is best between 6.5-9, and phosphorus is between 6-7. So even though coco is best at a lower ph you may still want to aim above the 6.3 range and hopefully that'll make everything available. Odd that its only affecting the one plant....but maybe the others are more resilient or other reasons.✌️