What are these spots?

[KristenReuel]

This Bifrenaria harrisoniae is under attack by something. It is only affecting the newest leaves, so I assumed it was a fungal infection, and sprayed it with a fungicide. But the new leaf that was hit the hardest kept getting worse quickly and the leaf has now dropped off. This leaf in the picture is the last new leaf on one of the two new psuedobulbs. There is no sign of infection on the other older leaves at all.

The marks are slightly pitted where there is black/brown, and all of the marks are clearly visible from the front and the back of the leaf. What is it, what is the best course of action, and should I cut this leaf off completely?

Thanks for any info!