oncidium everglades elegance brown spots

[Punysmurf]

Hello,

For about 8 months the bulbs on my oncidium everglades elegance have been slowly developing brown spots. currently it is affecting 2 of 5 bulbs, starting with the 2nd oldest bulb and now affecting the 3rd oldest. Both bulbs feel normal (firm). The bulb first affected started losing its leaves about 2 months ago. The oldest bulb (unaffected) has also lost its leaves. I’ve sprayed with alcohol, hydrogen peroxide, and soap spray at various points. It receives 3500 lux in a sunroom next to another oncidium which is fine and blooming right now. Does anyone know what this is and what to do, if anything? Thanks!