If you have opted to upload individual tracks for your content selection in your saved Project, you may notice a slight "lag" in the upload. (You will see a "down arrow" asking you to download the track that has been uploaded, in order to preview the track and approve it.)
If you refresh the page, it will resolve the lag and allow you to stream the tracks. You may need to refresh the page several times to resolve all tracks.
*Note - Refresh the page after each track resolves until all tracks are streamable.