Hard Cane Dendrobium brown leaf spotting and yellowing

[ViolinFin]

Got a new antelope hard cane dendrobium about a month ago. It's a den johannis x touch of gold hybrid.

Been getting these spots on the leaves and I have only been watering the substrate, not the ever wetting the leaves. The leaves affected appear to only be the bottom leaves. The two leaves I had that originally had it fell off.

I am also growing indoors on a south window on a 12th floor apartment in Seattle. It gets a lot of light, maybe too much at times? I also try to keep it near a humidifier.

What is this and how can I rectify it?