Smokey do you give extra magnesium (and calcium), they need a lot with so much light. I think red stems are normal and clawing is N overfert.
Definitely agree with your diagnoses of the nute symptoms, but my testing showed that it was unrelated to what the plants had their roots in.
I've played around with no food, more food, epsom salts, ph etc etc etc with a decent number of different plants. This is a clone I've grown for about 6 years now.
I think the light intensity was seriously fucking with the plant's ability to run chlorophyll in the top layer of growth. I think tissue testing would show exactly what was going wrong, but my theory is that the intensity meant the the plant was unable to process magnesium, sulphur or iron which lead to a cascading series of deficiency symptoms. There would eventually be compete breakdown and interveinal chlorosis would turn to necrosis.
As light intensity dropped the leaves straightened, newer stem growth returned to green, and chlorophyll flooded back into the healthier leaf tissue.
Hasten to add that this is not confirmed scientific fact. This is just one grower's experience with a single cloned variety. Perhaps hydro, a more competent soil grower, or different strain that wasn't selected for low light performance, would behave entirely differently. Perhaps spraying the foliage with a silica supplement could have helped protect the leaf's metabolic processes. Maybe the narrow cab and Mylar are no beuno. And maybe a bluer light source wouldn't have dumped so much energy into the top layer of tissue (3500k tested).
And of course, I don't have a light meter! Duh... haha. Too fucking easy!
At some point light intensity must be too much for normal leaf operation - my testing seems to show that in my tiny cabinet I was way over the limit with a single Vero 18 @ 50W.