Continuing from this WordPress.org support forum post - https://wordpress.org/support/topic/hidden-products-show-up-in-slider/
Woocommerce is up-to-date. Using a Storefront child theme called Deli.
- Hidden items
By Hidden I mean the Catalog Visibility is set to Hidden, which makes it so you need to know the URL of the product to actually visit the product page. It doesn’t show up on the shop page or in category pages, though. However, these items are still showing up in the slider.
- Sale items
Even though I have On Sale Item Display to No, sale items still show up in the slider.