The background issue is fixed as shown in the logs.
There is no “metalness” for refraction, so it’s working as expected, simply don’t use metal on your model. The alternative to ignore the metalness gives less flexibility.
You can use paint all while masking color/roughness to remove the metal paint.
Edit: by “expected” I mean how I wanted it to be. But the decision was more or less arbitrary, it depends from one software to another. I might change the behavior later but for now it’s not planned.