Did you use heavy magnification when you checked for bugs? I couldn't see any bugs under a 30x loupe last summer so I thought I was fighting a nute deficiency and nothing was helping. Then the guy at the hydro shop told me it was from mites. Early on in a broad mite infestation looks just like your pics and those little bastards are tiny. Took a 60x loupe and very strained eyes to see them. I suggest a 100x mic just to make it easier. If it is mites, then you're right, it is a nutrient problem but it's being caused by their phytotoxins.
Broad Mites really show in the new growth, narrowing leaves, clawing, and as the poisoning advances, a knarled look in new growth. I already had a full blown infestation by the time I took these pics and thought I was still fighting a nute deficiency.
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Even after I eradicated the mites the poisoning continued for some time since it lingers in the plant tissue. The damaged foliage never fully recovered but I had vigorous new growth again after enough poison dissipated.