The soil looks way too heavy and water retentive. And the plant is a little bit over potted.
This is a small growing Medinilla I have, Medinilla pendula, its a different species than yours but like yours it is also an epiphyte. It is thriving in nothing but sphagnum moss.
I would suggest to you that you may need to take your plant out of the container and look at its roots. I think that your plant has likely suffered significant root loss. If there are roots to salvage, I would replace the potting substrate you have with long fiber sphagnum, kept damp but not wet. You should choose a container with excellent drainage and only large enough to contain the root mass of your plant