I mean, usually when people have these issues theyre starting out but uve grown several years. Coco dont really go good with organics unless you specialize in it. This site doesnt have many people to answer to these things. Lots of soil and coco growers to get help from but we cant help much if its a mixed medium.
Id suggest doing either soil or coco not both. Coco is meant to be moist at all times, different ph requirements. Too much back always kills my coco plants so I imagine that would happen in this case. You dont overwater soil so the coco just dries and leaves issues. If feeding salt fertilizer it will spike as water evaporates. Just a long list of potential causes.