Okay so no water softener. And I know that you know what the hell you're doing, so there has to be something that is blocking the uptake of nutrients. I'm sure you've got the ph dialed in, and more than likely have checked the meter several times.
Are you adding any cal/mag? If there's no cal then N uptake is hindered. Your yellowing is in the new growth which is a micro nute def,,,, could be mag.
This is really weird and I'm grasping at straws cause I know you've done all the proper steps. I'll keep guessing. But I know you'll figure it out, when you do please enlighten us all.
OH OH another guess because it happened to me (got the same ugly necrosis and eventual death). Did you use a bug bomb in the room prior to starting this run?