Hello,

You have stretched the row and content and arrows are not visible in this case as there is no space for them: https://gyazo.com/443a1ed6eba482dbe99971af606a8f91

Please add this code to the Theme Settings > Custom CSS > Mobile/Tablet:

body .owl-carousel .owl-nav>div {
    visibility: visible;
    opacity: 1;
    -webkit-transform: translateY(0);
    transform: translateY(0);
    pointer-events: visible;
}
body .wd-carousel-spacing-2 .owl-nav>div[class*="next"] {
    right: -20px;
}
body .wd-carousel-spacing-2 .owl-nav>div[class*="next"]:after {
    right: -20px;
    background:rgba(255,255,255,0.8);
}
body .wd-carousel-spacing-2 .owl-nav>div[class*="prev"] {
    left: -20px;
}
body .wd-carousel-spacing-2 .owl-nav>div[class*="prev"]:after {
   left: -20px;
   background:rgba(255,255,255,0.8);
}

Best Regards