When displaying a slide, the slide will be rendered in stages.  You will see a status bar at the bottom of the screen showing you the overall status of the rendering.  The time it takes to completely render a slide will vary from slide to slide depending on the elements within the slide.  When a slide is being rendered, you can skip to the next slide by scrolling or by using the Next Slide and Previous Slide menu items in the contextual menu or Menu > View > Next Slide/Previous Slide