preview/play/export slideshow hangs

This has been a problem across multiple version and on both mac and windows.

When I go to preview/play/export a slideshow lightroom cc hangs after completing maybe 3%.  This happens maybe 1/3 of the time, and once it does I can no longer get things to work.  Past tricks were a) turning off h/w accel, or purging the video cache.  Neither works.

Super tired of seeing this.  Between a rock and a hard place now, as MSFT slideshow creator thingy doesn't run on the mac.

What's the secret to getting this to work?