Slider not working at WP 3.9.22

Hi,

While trying to use your plugin for inserting some sliders at my portfolio projects (and not only), the slideshow is not appeared at my front-end even if I can see it normally at my browser’s elements tab. I can only see the first image of the slider.

<div id="metaslider_2917" class="flexslider">
            <ul class="slides">
                <li style="display: block; width: 100%;" class="slide-2918 ms-image"><img src="https://samosbuilding.gr/newsamos/wp-content/uploads/2016/10/IMG_3.jpg" height="600" width="800" alt="" class="slider-2917 slide-2918"></li>
                <li style="display: none; width: 100%;" class="slide-2919 ms-image"><img src="https://samosbuilding.gr/newsamos/wp-content/uploads/2016/10/IMG_2.jpg" height="600" width="800" alt="" class="slider-2917 slide-2919"></li>
                <li style="display: none; width: 100%;" class="slide-2920 ms-image"><img src="https://samosbuilding.gr/newsamos/wp-content/uploads/2016/10/IMG_1.jpg" height="600" width="800" alt="" class="slider-2917 slide-2920"></li>
            </ul>
        </div>

Could you please give me some advice on this?

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