The leaves are showing signs of chlorosis (yellowing of green parts of plant due to chlorophyll breakdown which can be caused by pests, parasite attack, soil problems, shortage of nutritive substances and or moisture. If the new leaves are clean, this may indicate a fungus rather than a virus. If the new leaves also show chlorosis odds are being a virus symptom.
I would examine the plant closely for any noted pests, insecticide accordingly, a new round of soil would be helpful and a plan of weak weekly fertilizer will resolve if any of the above issues narrowing your symptoms.
The sheaths look very healthy but also can be cleaned a bit to prevent pests from hiding and or capturing water and rotting.
I am hoping others will chime in to narrow your catts condition.
My only concern would be to isolate your cattleya not knowing of its true condition as well as a new round of soil, if this is your option I would keep it in low indirect lighting for 3-4 weeks watering every 10-14 days.
Wish I had the answer for you....
Cattleya with dark spots on leaves
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