As this blog says there are new security policies on the way that will require the more secure https style links in all your storymaps and webmaps, and soon the plain old "http" type URLS may stop working.
To see if this affects your storymaps, log into https://storymaps.arcgis.com. At your list of storymaps, clicking on any of them may get you a list like that shown below, with a “we found some issues” warning panel at the left and a list of source URLS of problem images and the storymap section they were found in at the right. You can click on the image URL to see the problem image for yourself. As the list shows, these images are all accessed via an
