If a slide renders as an empty box with no picture, the image source is missing. The fix depends on your slide source.
Posts or products source
Slides built from posts or products use each item’s featured image. An item with no featured image produces a blank slide.
- Edit the post or product and set a Featured image.
- Items without a featured image are excluded from the query, so set one on every item you want in the slider.
Media Library source
- Make sure the image still exists in your Media Library and was not deleted.
- Re-add the slide if the image was removed or replaced.
For more on this source, see Build a Carousel from Posts or Products.