Yesterday ArcGIS StoryMaps deployed an update and spellcheck should be working again in most browsers.
Please note that spellcheck works differently in different browsers, so the experience may not be similar. For example, on some browsers you may only see spelling error indicators in a paragraph after you click to place the cursor there. In other browsers you might not see indicators until the cursor leaves a text block.
Please let us know if there are specific spellcheck issues that you run into.
Owen Evans
Lead Product Engineer | StoryMaps