I have created a Story Map using the Cascade template. I have added an Immersive Page and clicked the Add media button. I added an image (on a network drive) using the 'Browse to an image' button. It loaded successfully. Based on what I can see in the console the image is uploaded to our organization account on ArcGIS online. I shared the app to a group of users.
When those users attempt to edit the app the image I added does not get loaded. It just shows the animated loading gif.
Not sure if this is a bug or just a workflow issue.