As of 2019-11-27 Funnel will no longer export optional fields to Google Data Studio.
What is an "optional field"?
An optional field is a field available in one of your datasources schema but that isn't configured to be downloaded.
Why doesn't Funnel export them to Data Studio?
Optional fields will never have any data unless you change your datasource configuration
Data Studio will run smoother with less fields
What do I do if I've reconfigured my datasource and I still don't see the fields?
Refresh your fields in Data Studio as explained here