Sheet Summary Report not importing my Summary fields into "Columns to Display."


I'm trying to build a Sheet Summary Report, but my sheet summary fields are not importing into the "columns to display" section of the Report builder. All I see are "created," "created by," "modified," "modified by."

I'm sure I'm in the Sheet Summary Report. I'm sure I'm linking to the correct sheet. I'm sure the sheet has summary fields.

Has this ever happened to anybody? Is this a common glitch?