When a Masdevalia drops all the leaves...

[Salixx]

I got the same plant from Andy's. I keep it intermediate/warm but in a terrarium and mounted but it often is quite wet.

I would suspect lack of air circulation + wetness may have led to the decline of the plant. I am not sure you can bring it back, but if you try I would move it somewhere else.

I know a lot of people like to try to grow Masdies in bathrooms, but I am not a fan. I tried and did not see a good response. The humidity rapidly changes and so does the temperature when you take a shower. I think a lot of these plants can be acclimated to a variety of conditions but I'm not sure they like rapid fluctuations.

How much light was it getting? According to Andy's, this plant likes a bit higher light, closer to Oncidiums.