I have begun to think I just have deficiencys not nute burn. (unless someone can confirm)
Looks like deficiency to me. Are you testing soil ph either from runoff or a soil probe?
My first LED grow began magnificently, and went bad a couple weeks into flower. Looked a lot like yours. It looked like 3-4 deficiencies (sulpher, iron, nitrogen, magnesium). Turned out to be very acidic soil. (I don't believe it was related to LED. I changed nutes and I believe the nutes I used previously were buffered and helped hold a bad soil ph in a tolerable range, so I never knew I had a problem.
Anyway, that's what comes to my mind. I didn't get the scorch/burn/brown like a calcium or potassium. It was just an even die off of fan leaves which began as the pale symptom some of your photos show. Your mixed symptoms make me think ph lockout?
As mentioned, I found foliar feeding to be really helpful during that period.