Fixed
The bug has been fixed. See the Version Fixed and Additional Information, if applicable, for more information.
Workaround
To present the audio, use an existing Esri Story Map Tour created before June 26th. The story map created before June 26th can be re-purposed for an intended project.
The important date is the created date, not the last modified date. An unwanted demo or test tour created before June 26th can be used as the basis of the new Story Map Tour project to include the audio.
Use the embed code from the blog referenced.
If repurpose an old Esri Map Tour around the bug introduced in Esri Story Map Tour after June 26th, use the story map that does not use a hosted feature service behind the scene (for example, a Story Map Tour that is not created by uploading images directly from Web AppBuilder for ArcGIS) as the workflow uses a feature service in which the image is stored.