I have a Chiloschista and think your issue has been moisture. First it is not uncommon for them to occasionally send out a leaf. Having the leaf fall off wouldn't worry me, they use the roots instead of leaves to feed itself.

I grow in a g/h and water mine twice a day because the g/h in the winter is extremely dry. When you have a gas heater running almost constantly, very low humidity. I draped Spanish moss over my mount to help it hold moisture but it is still bone dry every morning and evening. The spike drying up also confirms the lack of moisture for yours. I would leave the roots alone. Just because they are black doesn't mean they aren't functioning. The "string" inside the outside root could still be sending moisture higher on the plant.

You could try the terrarium to help keep the humidity higher - it can't hurt to try to increase it. If it were mine I would lay some strands of sphag over the mount to help hold moisture longer. Don't put a mound on it but a few strips to keep it moist. If it is still sopping wet the next day, remove part of it. Letting the entire mount soak in water, roots down, would also help hold moisture longer.

I also give mine medium light - not Phal light but not Catt light either.

Hope this helps - Brooke