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...