Vanda/Renanthera Hybrid Issue

[FSUOrchids]

Not sure why this is happening all of a sudden, but my (relatively) new Vanda/Renanthera hybrid has started to yellow and lose a few of its lower leaves. I've grown several vandas before and I don't remember them doing this very often...

It's odd to be because the plant is growing new roots and new leaves at the top, which seems to suggest it's doing OK. I know they do drop leaves from time to time, but I'm not used to it doing this all at once. I'm hoping this isn't a cause for concern?

If anyone has any guidance here please let me know.