Hello Tilly
I had what looks like exactly the same a couple of years ago. The curved edges on the leaves and the dried out marks/lines on the leaves. I also found honey dew drops on the under perimeters of the affected leaves.
I never discovered exactly what pest it was but I did treat the plants successfully using advice from OB.
I bought pure Neem Oil and Horticultural liquid soap online as a package. Followed their directions for mixing and sprayed every surface of
all my orchids, tops of leaves, bottoms of leaves, stem, crevices and the top surface of the media they were in. After leaving in a gentle warm breeze for an hour I made sure all remaining liquid was removed from the crown and crevices so as not to encourage rot. (A piece of tissue folded into a point does a great job!) All the decorative pots, shelves etc also got a wipe down. I repeated this 3 times at weekly intervals to make sure I caught the bugs at all life stages.
The affected leaves don't look pretty but are strong and green - eventually they will become the oldest ones that drop naturally - in the meantime they are still doing their job.
In my environment there is a good chance the pest was a form of scale/mealy bug/cochineal.
Pure Neem Oil wasn't cheap but a little goes a long way. I haven't had any repeat problems but I spray every month or two, just in case. A bonus is nice bright, shiny, clean leaves!
Neem Oil has quite a strong smell, I quite like it but others don't. It disappears after a day or two!
Pictures show top of leaf, bottom of leaf, happy orchid x 2.
Good luck!