Vanda Discoloration Potential infection?

[UK Orchid lover]

I have had this vanda for about 10 years.

min temp= 19C in winter, Max temp= 30C in summer (degrees C)

Grown in a normal British home grouped with many other orchids. No other orchids in my collection have these marks.

It started about a year ago at the bottom of the stem on the lowest leaves and has begun to climb the plant very slowly.

Could this be a temperature issue? Age? or infection?

It is a very large vanda (noID similar to the pachara type)

There are no bugs present after close inspection and the roots are very healthy.

PLease help me