A possible fusarium wilt case on cattleya

[NYCorchidman]

Most likely fusarium.
You see that purple ring on the cut section of the rhizome? That's a classic sign, also your description fits.
Fusarium does not kill plants over night, but slowly progress and eventually kill. It can take years depending on how strong the plant is.

If you keep cutting the rhizome (using a different new tool each time you cut), you may find a spot, usually closer to the newest lead, where the fungus has not yet spred into.
That's the part you want to keep.
Throw away all the older infect parts along with old potting mix and the pot.