I am working on a shortlist beta Story Map and I've had this happen a couple of times now. Today I've updated the images at 2 locations. While the larger image loads the thumbnail is blank. The link in the URL is valid and I've even substituted in other images or even the larger image url link to see if it will even show a thumbnail and it seems hit or miss but mostly miss. I'm wondering if this is a known bug or what could be the issue if it doesn't give an error? The image names do have spaces and _ which I think should be fine and actually works for the larger image? Is there a bug with updating images/locations once they have had an image in place? Although even if I add in a new location the thumbnail will not show.
Also I've read it is recommended the larger images are 1000x750 pixels and have a resolution around 80% (I've went to 72) while the thumbnails are recommended to be at 280x210. The web folks at our agency think the application is slow because of all the images and the images being unnecessarily large at a size of 1000x750 while only displaying a smaller image. What are the image recommendations? I want the application to be as fast as possible and not slowed down by the images being too large.