Thanks to @AsNoriu, I am now of the opinion that I am dealing with a Potassium excess. Not seeing any issues with older/lower leaves, strictly yellowing and slow growth of fresh new growth. Going to attempt to snap the plant out of it with a healthy watering of plain rainwater. Barring that, I think the scheduled transplant over the next 7 to 10 days might help "re-balance" the soil.
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