Maybe p-deficiency? "bare minimum nutes" isn't enough to give a proper guess, and some people's idea of mnimum is a lot :P but, if you look at a leaf symptom chart, you'd see why i made this guess.
Old leaves can get mottled or show some issues, but this looks a bit more than that.
is the substrate repelling water? if so, you need a wetting agent / surfactant (same thing). Lots of options there.
VPD impacts rate of drinking. So, if vpd dropped recently, drinking by the plant would slow too. Tends to happen if you don't have a humidifier. The large plants transpire quite a bit more and add significant moisture to the air.