This item has been identified as an outstanding known issue. A workaround is provided until the issue is officially fixed.
Column headers are missing when exporting in Tabular Multiple Column with no dimension on columns.
Issue can be worked around by either of following methods:
Use Tabular Singule Column
Rearrange pivot so at least one dimension comes to column
If this workaround is not suitable in your use case, please contact Support at firstname.lastname@example.org.
Internal Reference: CORESRV-4496