I have a MacBook running 10.12.1 Sierra. I upgraded the version of Lightroom so that I could download the new Canon 5d Mark IV files.
The slideshow doesn't work now. When I try to play the slideshow I get the dreaded black screen.
Any suggestions would be more than welcome. I use this feature at my weddings and time is limited and it's frustrating that it doesn't work.
Have you tried turning off the GPU from the Lightroom preferences?
Open Lightroom > Edit Menu > Preferences > Performance tab > Uncheck the GPU > Restart.
There has been a fix for black slideshows in 2015.8. Please update to the latest 2015.9 using the update function from the help menu or download from here: Download Photoshop Lightroom