I'm sorry, I didn't see this question when posted in December 2021.
Bulbophyllum stramineum is now considered a synonym and the correct name is Bulbo. cummingii. You might find more information with that name.
The first thing I see is the plant is very dessicated and wrinkled. The leaves and pseudobulbs should be smooth and shiny when well hydrated. It is in large bark, and it is very dry. When Bulbos get dessicated they get large black spots, and entire growths may turn black. I think this is the problem with the plant in the picture. It looks like a rot but instead this is how Bulbos act when too dry.
Bulbos of all sizes have much thinner and shorter roots than other orchids. This means they take longer to absorb water than do many other orchids. They expect to be very moist to wet, and the roots should not dry out for any length of time. I wouldn't try to grow them in large bark; I prefer sphagnum moss, which I keep always wet. Some people grow them in fine bark. But the roots should always be moist.
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