Brassia leaves turning brown

[Vespucci8]

Hello all,

Wishing you a happy new year and lots of luck with your orchids.

I have a question regarding my Brassia. A couple of her leaves are turning brown. The picture shows three leaves with brown spots that turned into this state in about 1.5 month.

I water it once a week when the wooden stick is almost dry. Temprature is around 19 Celsius (66.2 Fahrenheit) and humidity is 50%. The orchid is standing on a bench next to an eastern window with a see through curtain.

The pseudobulbs look fine to me and there are no yellowing leaves. Do you know what I am doing wrong?