When an object with dynamic refraction covers another transparent object, the object behind disappears. It's my understanding that this is because refraction is done in a single grabpass, instead of once per object. While this works for simple objects, it's a serious limitation for scenes with more than one refractive object (or other transparent objects).
A real-world example is this shower panel, where we can't currently use refraction & attenuation, even though we want to.
Test project: https://playcanvas.com/project/1460696