Slide Transition not working with Ken Burns
When Ken Burns is enabled for a slide's main background, the slide's initial transition will always be "Fade In".
There are many options for a slide’s main animation as well as the Ken Burns effect. And because of this, these option-sets are separated. But a Ken Burns transition is technically classified as one of the slide’s available main animations. So when the Ken Burns effect is chosen, it can’t be combined with a second animation.
When the Ken Burns effect is chosen, the image will always fade in before it pans/zooms. So in essence, when the Ken Burns effect is enabled, the slide’s initial main animation will always be a “Fade In”, and then the image will start to pan/zoom according to your Ken Burns effect settings.