I don’t know why but I needed to change it on the css file on the plugin located on
/wp-content/plugins/portfolio-slideshow/src/resources/public.css
Where appears
.showloader .portfolio-slideshow, .showloader .slideshow-nav, .showloader .pager {
visibility: hidden;
}
Change for
.showloader .portfolio-slideshow, .showloader .slideshow-nav, .showloader .pager {
visibility: visible !important;
}
