recently i noticed that my newest orchid growth had a problem. By looking at the photos, it looks like it may be leaf spots but I would prefer to have the opinion of someone who has more expertise in these matters than me.
I agree; the roots look perfectly fine!
How much sun is the plant getting? Fertilizer?
I would be thinking mechanical then.
As long as the rest of the plant is looking okay and the condition is not spreading, I'd just wait it out.
I had this happen to two of my catts. last year. I have no idea why, but this year the new growths were fine. From what I can see in the pictures, the rest of the plant looks healthy. I'd twist that leaf off, it's not doing the plant any good any more. Keep us posted.
I'm not sure the amount of sun that the plant is getting because I don't have an instrument to measure lumens or any other measurement of light. I can tell you that I've had this plant for at least 4 years and it should be the same amount of light that it's been getting every other year because it's sitting in the exact same spot in my window that it was last year and the year before. It's been receiving the same amount of fertilizer too. I use the sunbulb orchid fertilizer from my local Lowes store and I use the recommended amount on the bag. I have around 50 various orchids and none of the others seem to be showing any problems.