We've seen this happen occasionally when authors copy and paste content into Cascade, particularly from other websites. Looking at the app data behind your story, I think that's what's happening here as well.
When you copy-paste, sometimes invisible symbols and characters get copied and pasted along with the stuff you can see. There are a few invisible characters -- in particular line breaks -- that will screw up the application data and Cascade won't be able to process it.
See this other geonet post for steps to solve this problem using ago-assistant:
My story map wont open after I made it. It just shows the loading sign. I have tried it on different...
The phrases I'm seeing in your app with these invisible characters are listed below. I've put *** in where the problematic characters are -- many appear at the end of a phrase, after a semicolon. You should be able to use ago-assistant to remove these characters.
consisting of terabytes or peta- bytes of data;***
being created in or near real-time;
***
temporally and spatially***referenced;***
striving to capture entire***populations . . . traditional, small data studies;***
aiming to be as detailed***as possible
conjoining of different data sets;***
