tomjonesrocks sent in an email to the support team and we were able to find that these CloudFront URLs are appearing due to a bug. More specifically, setting the text of a widget to text that ends in an image file extension will show a CloudFront URL.
As a workaround, we removed the image extension from the text in the repeater's data set. Then we added the image extension to the repeater's OnItemLoad event. As shown in the screenshot below: