Bulbophyllum Elizabeth Ann Buckleberry leaves suddenly deteriorating

[greenochre]

I got this Bulbophyllum Elizabeth Ann Buckleberry in December, and before very recently it looked happy and grew a new bulb. I had it in the coco fiber basket with sphagnum mixed with perlite and leca

About two weeks ago when watering I noticed some roots became mushy, so I took it out of the basket and discovered it lost half of its roots, they became mushy and velamen stripped from them.

I thought it was a root rot meaning I was able to overwater a Bulbophyllum (facepalm). So I removed old sphagnum (it was all dark green with algae), add some fresh sphagnum and reduced watering a bit.

Then a few days ago, leaves on the two seemingly the oldest bulbs turned half-yellow overnight, I though maybe reducing watering was a mistake, gave it a good soak and went back to my previous watering schedule (misting daily, good soak 2-3 times a week - I live in Barcelona and indoor humidity is pretty hight here, so it never dried up with this schedule).

But leaves continue deteriorating and in three days they became black and snapped out

I checked roots again and I saw that only the newest bulb has plump good looking roots now.

Clearly, something was wrong with either potting or watering, but I don't know what and what I should change..?
Also, are the bulbs that lost leaves dead? or they still could produce roots or new bulbs?

First two photos are taken on the day leaves yellowed, and others three days later

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