YouTube widget has stopped working in Captivate 9

I have several web pages with embedded YouTube videos that I created in Captivate last year, and they're working fine. Yesterday, I updated one of them (using Captivate 9.0.2.437 and MacOS 10.14.6), and now the YouTube videos do not show up. There is just a big blank area where the video should be. I get the same thing whether I create an HTML5 page and view it in a web browser or use Captivate's Preview function. All other features of the web page appear to be working normally.

All the pages I created previously are still working, so this doesn't seem like it's a problem with the YouTube API (like the problem that happened a couple years ago). And it happens even if I take a project that worked before and simply repeat the process of creating the web page for it.

Is anyone else having this problem? And does anyone know of a solution?