Wilsonara dark spot on new growth spreading. Rot?

[Student Hobbyist]

Hello, I have had this Wilsonara for a couple months now and up to this point it has given me no problems. It is potted in sphagnum moss in a plastic pot with ventilation slits on the side.

It came to me with very little roots, but has adapted nicely to my plant room (or so I thought) and has even been working on a new pseudobulb.

Over the past week however, I have noticed a dark spot on one of the leaves associated with the new growth. I am aware that some orchids can have a dark pigmentation in their leaves that is completely normal but this has me worried. It has continuously spread up and down the blade of the leaf from where it started.

*please see attached photos*

I am worried that if it is a disease or fungal problem it will spread to the rest of the plant and kill it.

Can anyone advise me on what this spot is and if its is threatening to the health of my plant? If it is should I simply cut the affected leaf, or should I be more drastic and cut away the entire new growth so it doesn't spread to the rest of the orchid?

Thanks for any advise.