Slider Images Not Visible

I’ve followed the instructions below :

Select the “Image Slider” from the Choose Home Slider options.
Expand the toggle box and select an image from your media library.
Use the “Title” field to add a main message to your slide.
Use the “Description” field to add additional information to your slide.
Use the “URL” field to select a page from your site to link the slide.
The slider will display a “Read More” button if the “URL” field is set.
Repeat the above for each additional slide you want to add.
Don’t want a slider? To disable the slider entirely simply press the “Disable” option.

But the page never shows the images, no matter what size I use, what type etc. The text is shown, the description is shown, the More Info button is shown, just the pictures. What am I missing?

I’m afraid I can’t provide a link to the page because it’s an internally hosted intranet page.