Missing Download link after XML export

After performing the XML export of a whole Space, the progress bar stops goes all the way to 100%, but the status message hangs at Writing export and the Download link never appears (see screenshot). The archive is created correctly, though, and can be retrieved from the file system. Customers can't access their backups without assistance from Support.

Note: on the same instance, after exporting a smaller Space or a custom, limited export of the same Space, the link appears as expected.