kraweb
Hi,
The point is the browsers don't support that background-attachment: fixed; property in iOS, as I can see in the template, the background is set with special style for ios so that the image, at least, can display fine:
.is-ios [data-type="background"] {
background-position-x: 50% !important;
background-size: auto 100% !important;
background-attachment: unset !important;
}