Section Missing on iPhone Browser

i too can not see the reason for it
on the code i do not see any setting for screen element visibility. As you can set on Advanced Tab of the testimonial element itself.
But i do see your testimonial on an iphone 8
maybe it is on your end a caching problem – go to your iphone settings – safari and empty the browser cache.

by the way : can you have a look on your testimonials if you set up this to your quick css:
(you had to download the “3d shadow” from my server – and change the url in the css – but for first test it will work )

.av-large-testimonial-slider .avia-testimonial_inner {
    background-color: #ecf6ff;
    display: inline-table;
    padding: 40px;
    border: 1px solid #aaa;
    position: relative;
    box-shadow: 0 3px 10px -8px #333;
    -webkit-transform:  skew(-3deg);
    transform: skew(-3deg);
}

.av-large-testimonial-slider .avia-testimonial_inner::before {
    content: "\e833";
    font-family: entypo-fontello;
    font-size: 70px;
    position: absolute;
    top: -15px;
    left: 15px;
    -webkit-filter: drop-shadow(2px 2px 3px #666);
    filter: drop-shadow(2px 2px 3px #666);
    color: #3579b4
}

.av-large-testimonial-slider .avia-testimonial_inner::after {
    content: " ";
    background-image: url("https://webers-testseite.de/wp-content/uploads/testimonial-shadow.png");
    background-repeat: no-repeat;
    width: calc(100% + 60px);
    height: 100%;
    position: absolute;
    left: 0;
    top: 0;
    background-position: bottom right;
    overflow: visible !important;
    background-size: 60px;
    opacity: 0.3;
}

#top .av-large-testimonial-slider .avia-slideshow-arrows a {
    margin-top: 50px !important;
}

.responsive #top .av-large-testimonial-slider.avia-testimonial-wrapper .avia-testimonial {
    padding: 0px 10px;
}

.responsive #top .avia-slideshow-controls a {
    display: block;
}

.avia-slideshow-arrows a {
  overflow: visible !important;
  text-indent: -5000px !important
}

.avia-slideshow-arrows a.prev-slide::before {
  left: -110px;
}

.avia-slideshow-arrows a.next-slide::before {
  left: 80px;
}

see here: https://webers-testseite.de/testimonial-styling/