Do you know how long the plant has been in that moss? It looks rather old to me. With the rapid drying you mentioned, it is possible that minerals from your water and any fertilizer or additives you may use have built up to the point of being toxic. (In my growing conditions, sphagnum needs to be replaced about every 6 months or so.)
I would recommend getting some nice, fresh potting medium of your choice , and
following this procedure to recover the plant.