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?