OK… I think I’m finally got to the bottom of this.
Not hiding the sphere is the thing that’s done me in. If you follow as per video and select all with everything showing and clear seam while live unwrapping is on then this is what causes all the squares.
Hiding the sphere completely and keeping the eyes. brows and mouth hidden until you’ve completed the unwrap of the shader is vital! The importance of this really isn’t stressed in the video.
How do you remove the UV map from an object e.g. the sphere if you do it by mistake?
