Disease Spots on Bulbophyllum Carunculatum

[Oanadani]

I have noticed that the leaves on my bulbophyllum Carunculatum get these spots and then slowly turn yellow /brown and fall off. One by one.
It already lost 3 leaves in autumn and now I see 3 more leaves affected. The bulbs seem fine, but I can't help think it's a disease of some sort. I've had the plant for a few years and this only started this autumn. It also bloomed in autumn and now I see it has 3 new growths so I don't know what could be wrong.
Attached are pictures of the leaves, the bulbs and the healthy leaves too.