Yikes! I would suspect a combination of some nutes and you may even have some mites in there. I'd hit it with some nice fish emulsion and maybe some Cal-Mag. Just a suggestion.
You cant figure it out seems like you tried everything already leading to what looks like nutrient burn on that big leaf in the center.
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Half that leaf looks dried and crispy.
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Also looks like an overwinter that needs a new pot, new soil, new lime.