I'm not sure if I should be reporting them to SIDEFX support, but I'll start here. Totally understand that this is still in experimental stage.
But... here's the same scene with the same node selected - in OpenGL and Vulkan. Feather shapes look completely different on Vulkan. No background display visible either. No colors...
This is on the latest daily build. Note in the OpenGL view I just turned on point display to show where the actual 3d feathers were.