Den Atroviolaceum yellowing leaf, need advice

[twentyseven]

So far I haven't found any evidence of bugs, no white fluff or evident of leaf damage. I would say this would be the second newest leaf, (there is a smaller cane with another leaf and then 2 more new canes with no leafs yet.) the leaves on the older canes look nice and healthy. What struck me as weird about this yellowing leaf is that it doesn't look mottled or damaged in any way, it just turned bright yellow overnight.

The tips of some of the roots are starting to creep over the edge of the pot. I've dug up a little of the bark and it looks like the roots I have found so far are ok, but I'm new at this so maybe I'm not the best judge.