I am running Houdini 18.0.499 and new Octane X for Houdini on an iMAC. The GPU supports METAL. When I setup a simple scene in Houdini and run the Octane IPR, I get a message that the scene cannot be rendered because it is too complex or that I do not have enough GPU memory. The scene is simply a sphere and an octane light. I have 8 Gbytes of GPU memory. What am I missing? Also, I am running Catalina 10.16.6, the latest required version.