Diagnose my roots... Please.

[OrchidThief79]

I have a Neostylis Lou Sneary potted semi-Japanese style in sphagnum moss in a clay pot. It sits outside (in Hawaii) in bright shade. I water it about every three days, so the moss is almost always completely dry, at least on top. Sometimes it stays dry longer. I fertilize weakly weekly.
As you can see in the photos I've attached, some of the roots on top of the medium have become rather shrivelled and dessicated-looking, some turning a brownish color. They are hard and not mushy.
I have three hypotheses as to why the roots look this way:
1) Underwatering: I'm simply not watering it enough and the roots have dried up. I'm leaning toward this..
2) Fertilizer burn: I've either over-fertilized or let too much salt build up in the medium. I don't really know what burnt roots look like.
3) Overwatered: The moss has stayed soggy for too long and the roots rotted. I tend to doubt this, as the roots in question are exposed to the air and the medium rarely stays wet for more than a day or two.
I would greatly appreciate your insight! Thanks.