You have created a Nurture Engagement Program and are running an Engagement Stream Report, and a stream is not showing on the report.
One likely cause for the stream not showing on the report is that the stream is not sending out content. Once the content in the Engagement Stream is being sent (cast), then the email activity will begin to show on the Report.
In order to cast content, the cadence must be set. If the Stream Cadence has been set, and the Stream is still not showing on the Report, another likely reason is that there are no Leads in the Stream. The solution here is to add records to the Stream.