How much sunlight is it getting? How fast does that soil dry between waterings? More sunlight and less water may help your Hoya to stop dropping what's left of its leaves.
Looks like a lacunosa they tend to get overwatered so easily and rot as well. Looks like it got over watered. My advise is to water the prop into the soil when you first prop it and then after that just mist the soil every other day or every couple days .