Paph. delenatii leaves dying

[CROrchid]

So, I've ordered quite a few paphs over the last year and they're all doing well so far..except for delenatii.

I bough the plant and it had 5 leaves. In some month and a half the bottom two leaves died and the third one is in process right now. They first go somewhat limp (not sturdy like other leaves) and soft. They start yellowing...then they turn brown, crisp and dry.

The plant is not in a transparent pot, so I can't see the roots without unpotting.

The plant is on a northern windowsill, right next to a brachy hybrid, Paph. Magic Lantern and Paph. Envy Green, all of who are growing very well and not showing any issues. I water the plant every 4-5th day, it's planted in bark. The room temperature is cca 20-24*C, humidity is not very high, 40% perhaps. I sometimes open the window for 15mins to cool down the room, but not too often, maybe twice a day during daytime.

What could be happening with the plant? Should I repot it? (I can attach photos when I'm back home and update the thread)