Hi,
If I set any value or put an image into the Metallic pin in the Universal Material node, Octane will stop rendering. You have to set the Specular pin to zero to get the Metallic setting to work. If both Specular or Metallic are above zero it will stop Octane from rendering. To get it to start rendering again, I have to set the viewport shading to Wireframe or Solid and then change it back to Rendered.
Jason