Videos Within Slideshows No Longer Play

I've made several slideshows in the past week from our recent trip to South America (and many from past trips), and each incorporates stills as well as a music track and videos. Some of the videos are from my iPhone and some are from the Canon 5D Mark IV.  In the latest slideshow, the videos don't play - they just display as if they were stills. I have not changed any settings, or updated any software since the videos I made last week which all worked fine.

Has any one else encountered this problem? Suggested solutions?

- LRC version 12.0.1

- Dell Desktop running Windows 10.0.1

- 24 GB RAM