I know I've seen this question before - and I know it had been resolved by another grower's answer... I seem to remember it had something to do with overwatering but I'm not entirely certain that's possible here as you're growing in coco... Your EC seems to be a little high for an autoflower - but whether or not that's contributing to this problem or not, I really don't know... Going to follow this one AND your grow because I want to learn!
Good luck....