Joanna,

I tend to agree with Kenni and Deg about the moss being packed too tightly,
but there is one more possibility. I know that your plants are in close
proximity to one another, but each one still has its own micro climate. Is
it possible that this plant is a bit shielded from air movement, even a
little?

As you may remember, I grow outside under screening. A week ago, a Phal
began losing its leaves for no apparent reason (not crown rot - I know what
that looks like!). I pulled it out of the pot and found it soaked and
rotting, while three others right around it are fine. For whatever reason,
it wasn't drying out in that spot.

Diana