Being that I'm a novice it may not hold much weight but all I can think to say is couldn't it be nitrogen toxicity? Could be pH like you said those issues at the roots can look like a lot of stuff.... hmmm just read some of the earlier stuff while writin this looks like resinhound thinks its nitrogen toxicity too. Just curious if you did a flush in between your feedings since you noticed the nitrogen toxicity even cutting back on the nitrogen won't do all that much if there's already an abundance of it in the soil gotta get rid of it with some pH'd water then run some nute water through it kinda clean the slate a bit? Just my two cents of course, I could be wrong I'm no pro lol