Cymbidium ensifolium yellow leaf, black spot on pseudobulb

[Conjuration]

Hello!

I got the Cymbidium ensifolium in question last September. It came barerooted and immediately went to semihydro (leca medium, net-pot-cache-pot system). Since then it has grown a new pseudobulb to maturity and is currently growing another.

A few weeks ago, I noticed a leaf of an older pseudobulb had signs of chlorosis and began to yellow from the center. I thought it's getting too much sun and moved it where the leaves wouldn't get direct sunlight.

Today, I discovered the same yellowing leaf had yellowed down its stalk (is that the right word?). So I peeled back the pseudobulb's outer covering to discover a rather large black-brownish spot on the pseudobulb.

The spot was firm to the touch. I have no idea if that spot was there when the orchid first arrived, so I don't know if it had any correlation with the yellowing leaf.

I know cymbidiums shed the leaves on older pseudobulbs in time. But the pseudobulb with the black-brown spot and yellowing leaf is not the oldest of the plant (that honor belongs to the pseudobulb just behind it), and that's why I'm concerned.

Any advice/suggestion/comment? This is my first cymbidium, so I have no idea what to expect here!

P.S. I don't know if its relevant. But also a few weeks ago, the cymbidium in question started having a bit of root problem. There was some semi-transparent, snot-like stuff around a few of the roots submerged in the reservoir and sort of oozing out of the net pot.

I rinsed the outside of the net pot under running water and removed the snot-like stuff sticking to the outside of the net pot. It didn't stink so I didn't treat the plant any further and just did my normal watering routine.

In the following weeks, I rinsed the outside of the net pot every time I watered to get rid of the snot-like stuff, which, thankfully, continued to decrease in volume. As of last watering, the snot-like stuff appeared to have stopped spreading.

Of attachments:
Picture 1 and 2 are of the pseudobulb. Picture 3 is of the orchid. Picture 4 is of the affected leaf.