The file will download automatically when done, and then you will be redirected.
Registrations report started successfully…
SyntaxError: Unexpected token < in JSON at position 1
An error occurred and the job has been stopped.
What that could be is the response contains a PHP Warning or Notice in the response body when the Content-Type:application/json; charset=UTF-8 header is set.
If you go to your WordPress Dashboard’s Tools > Site Health page, does it show a warning about the site being set to display errors to site visitors? If so, you can click the arrow link next to the warning and it will have more information about how to configure debug mode.