Lazyloading images in horizontal slider

I am lazyloading the images on this site with jquery lazyload and a treshold: https://bm-translations.de/#leistungen

//Lazyload Images with Threshold https://www.appelsiini.net/projects/lazyload
$(function() {
    $("img.lazy").lazyload({
        threshold : 400
    });
});

So Images src is replaced by data-original. When I scroll to the element it should change it to src, as it.

But out of some reason its loading the images in the bootstrap-slider too slow (when I click to it or its autosliding some images havent loaded), as you can see. How to adjust this code, so its working for this as well?

The slider has a general structure like that: https://www.w3schools.com/bootstrap/bootstrap_carousel.asp

Carousel JS is:

$('#myCarousel').carousel({
        interval: 9000,
    });

    // handles the carousel buttons
    $('[id^=carousel-selector-]').click( function(){
      var id_selector = $(this).attr("id");
      var id = id_selector.substr(id_selector.length -1);
      id = parseInt(id);
      $('#myCarousel').carousel(id);
      $('[id^=carousel-selector-]').removeClass('selected');
      $(this).addClass('selected');
    });

    // when the carousel slides, auto update
    $('#myCarousel').on('slide.bs.carousel', function (e) {
      var id = $('.item.active').data('slide-number');
      id = parseInt(id)+1;
      $('[id^=carousel-selector-]').removeClass('selected');
      $('[id=carousel-selector-'+id+']').addClass('selected');
    });

I tried this, but then it wasnt sliding anymore:

$('#myCarousel').carousel({
        interval: 9000,
        scroll: {
            onBefore: function( data ) {
              var $current = data.items.visible.first(),
                  visible = data.items.visible,
                  src = visible.data('src');

              visible.attr('src', src);
            }
        }
    });

How to fix it, so its either lazy-loading before click/autoslide or at least to lazyload the whole carousel images with threshold?

I suggest you use the "owl.carousel.js" plugin. It is much better and has more features.

$('.owl-carousel').owlCarousel({
    items:1,
    lazyLoad:true,
    loop:true,
    margin:10,
    autoplay:true,
    autoplayTimeout:3000,
    autoplayHoverPause:true,
});

<link href="https://owlcarousel2.github.io/OwlCarousel2/assets/owlcarousel/assets/owl.carousel.min.css" rel="stylesheet"/>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://owlcarousel2.github.io/OwlCarousel2/assets/owlcarousel/owl.carousel.js"></script>
<div class="owl-carousel owl-theme">
    <img class="owl-lazy" data-src="https://placehold.it/350x250&text=1" data-src-retina="https://placehold.it/350x250&text=1-retina" alt="">
    <img class="owl-lazy" data-src="https://placehold.it/350x250&text=2" data-src-retina="https://placehold.it/350x250&text=2-retina" alt="">
    <img class="owl-lazy" data-src="https://placehold.it/350x250&text=3" alt="">
    <img class="owl-lazy" data-src="https://placehold.it/350x250&text=4" alt="">
    <img class="owl-lazy" data-src="https://placehold.it/350x250&text=5" alt="">
    <img class="owl-lazy" data-src="https://placehold.it/350x250&text=6" alt="">
    <img class="owl-lazy" data-src="https://placehold.it/350x250&text=7" alt="">
    <img class="owl-lazy" data-src="https://placehold.it/350x250&text=8" alt="">
    <img class="owl-lazy" data-src="https://placehold.it/350x250&text=9" alt="">
    <img class="owl-lazy" data-src="https://placehold.it/350x250&text=10" alt="">
    <img class="owl-lazy" data-src="https://placehold.it/350x250&text=11" alt="">
</div>