Possible reasons

• JavaScript errors occurr which prevents the whole site from executing JavaScript. Without JavaScript, no images will appear. That error need a fix.

• To verify that there are no JavaScript errors on your page do this:

  • open the site in your browser
  • Chrome: press F12 to open the developer tools
  • switch to the Console tab
  • check if there are any warnings
  • if the console window is empty, you’re fine