One way to solicit feedback from external collaborators on a StoryMap is to send them the URL to the story, along with login credentials for a temporary account on the organization hosting the story.
If a collaborator happens to be logged into their own, different ArcGIS Online organization in their browser, and they click on the link to open the story, then they are directed to the generic "Hmm... there seems to be an issue" page. Users often do not understand the "issue" is that the account they are already logged into does not have permission to view the story. (They can -- but typically don't know to -- use an incognito/private browser window or logout of their account first, and then open the link.)
Perhaps when a logged-in user visits a StoryMap URL to which they do not have access, then the system could provide that information clearly as the error message, and guidance on how to potentially resolve the issue. For example, it could let the user know that "Your account does not have permission to access to this story," and offer the user an option to login with different credentials or switch accounts.
