If I try to open the model with Unity5 template, however, I can load the model. I cannot change paint any color on the model - only height - the project opens as a read-only file.
After saving the project with a different name, the project now opens normally, however, the same issues are present - no color changes - only height - are visible on either the preview material or on the model.
And finally if I then change the shader on this file to PBR metal with anisotropy, then the model turns white and nothing can be painted on the preview material or the model.