I suspect this is a bug and have a case with Esri support for it, however, I thought I would share it as an FYI with the community.
If you create bulleted text in a Google Doc, copy it, and then paste it into a text block in StoryMaps, it appears correctly as bulleted text. If you then Preview, Publish, or otherwise cause the story to reload, then that text disappears. If you exit Preview, or return to Editing from Publishing, then the text is still gone, and cannot be recovered.
Workaround: after pasting the text into StoryMaps, immediately select it, and explicitly set its formatting to "Bulleted List".