Last tested: Jan 17, 2019
If you are exporting a Look publicly in a Google Sheet and use user attributes in your LookML, the public export will use the default value of the user attribute. This may be different that the exporter's user attribute value.
If you have no default value set for the user attribute, with the =ImportXML function like "Imported content is empty"
The error with the =LookerFetchData function is more helpful and lets you know about the lack of default value in the user attribute.