Yellowlab's hidden images test result
When the Hide on feature is being used on our sliders, Yellowlab's "hidden images" test result currently lists all our images next to this message:
List of all images that have a display:none property, or one of their parents. These images are loaded by the browser even if they're not visible. You might be able to find a way to lazy-load them, only when they get visible.
They are correct about the part, where display:none is being used on the parent, but your images are not loaded by the browser and they are lazy loaded to only load when they become visible. On slide background images we are are using loading="lazy" attribute, which does exactly what they want. This attribute is supported by all modern browsers, just in Safari you have to enable it as it is an experimental feature for them, but they will support it in the future. So maybe in Safari you can say that this message is appropriate, but it won't be for long.
You should ignore this message, as Google does recognize this solution. You can see here how they are suggesting using it at the "Native lazy-loading for images and iframes" part.