You might want to contact the author Contact the Basin and Range Dark Sky Cooperative (brdarkskies.org).
That happened to my story when I was actively editing it.....I have a support ticket in to Esri and so far there is no explanation given. I hope that the story is not lost but I suspect it will have to be redone-- I had to totally recreate my story as my original one has had the same message for weeks.
I think this is not your story (from how I read your post) but I recommend anyone making story maps with this new website (yes I am late to the party) make a few backup copies if one gets hosed....you don't want to be SOL when people are counting on your stories to support their work. My more than two cents anyway...
Let me know if anything happens! I am having this same problem.