Follow the steps below in order until the issue is resolved:

  1. Remove the entire field set from the export and re-add it
    1. Note the fields and related criteria of the output in that field set (category of the field)
    2. Remove the entire field set of the affected field
    3. Save and close the Export
    4. Open the export and confirm the field set is no longer there
    5. Add the desired fields back to the export and save it
  2. Recreate the query