I have updated my Blender for the adding clearcoat, sheen, etc. There is a regression, however. If you have a working exporter version of Blender 2.80, do not update it until exporter 6.1 comes out.
I do not know, if this is just a last minute api change, or some temporary problem. If an API change, will not be updating 6.0, since it was never production to begin with.