That is a beautiful plant.
I am just guessing here but there does not appear to be any drain holes in that container. I suspect it is holding too much moisture. Others with more knowledge will chime in with how to check the roots and re-pot.
Also, I may be way off base here but the willow twigs are giving off salicylic and indolebutyric acids which would aid in rooting for terrestrial plants but I am not sure if they help or harm non terrestrials like those in the orchid family???
