Owen,
Yes I did contact Customer Support. Here is the re-cap for anyone else encountering this issue:
From ESRI Support:
You were experiencing issues with your StoryMap not displaying images in ArcGIS Online. Your StoryMap was originally published in your Enterprise Portal, and shared with your ArcGIS Online organization via a Distributed Collaboration. When taking a look at the web traffic, we found 500 level errors when the request was made to display the images from the resource folder.
My thought was that the distributed collaboration was not sending all the images over (missing in resource folder), and that was why we were seeing the errors. First, we tried to un-share and re-share the StoryMap to see if this would fix the issue, and we found that most of the images now showed up.
Our next step involved using ArcGIS Assistant. Please note that ArcGIS Assistant is not supported by Technical Support, and it is recommended that you only use this in special circumstances when advised by a technical support analyst. We navigated to the StoryMap item's resource folder, and sure enough the images that were missing in the StoryMap were not present here.
We added the images to the resource folder, making sure to use the same name of the image that the request was using (long alphanumeric string). After adding all of the missing images back, we were able to see all of the images in the StoryMap successfully.
