After CSV export the field reporter for some users not all of them is code: ef0b01ea-6e64-4aa0-abbb-0608dcd10717.
Why for some of the user the name is show and for some of them just code.
Im using Jira Sheets or Excel integrations to download the displayname (reporter.displayname) or reporter email when needed
From search issues is not possible to download this data.
https://integrations.atlassian.com/
you can edit the fields to export directly from the add-on configuration.
I hope this helps you.