Slideshow Effects do not work in Video export

Hello

I build my first screenshow (31 photos) with music & transition effects. All looks great when played in Lightroom, but when I export as video I see the photos and music is playing , but no transition effect takes place ... tried each export quality with no difference . I am work on a 2015 macbook pro with max RAM & pro graphic card.

Any idea what is happening ???

Regards Bjoern