A Blackbaud Sphere user has created an email in Communications > Email. They saved the Receivers query as a list and sent the mailing. The Receivers query is not a link, but instead just text reflecting the name of the saved query. The Receivers queries in their mailings have all been links except for this one, which has the user concerned.
When you save a Receivers query for a mailing, you can save it in two places. The first is to save it for the mailing, the second is to save to the Query Library. If the user saves the query to the Query Library, it will be available for viewing after the mailing is closed. If the mailing was not saved to the Query Library, it will not be a link and can't be viewed later using the Receivers link.
As a workaround, you can hover over the name of your mailing and click Reports. The list of those included in your Receivers query can be viewed by clicking View Report next to "Total Records in Query/Subscriber Base". (Note: You may need to click "Update Report" at the top to see the latest statistics)