Videos not playing for web attendees

I've taught many webinars using the same keynote presentations that have several 60 second to 5-minute compressed videos and the videos have worked fine.

But today, while the videos played fine on my computer, most of the attendees said the video visuals froze after a few seconds and only the audio continued. The same happened when viewing the vids on my other computer that's used as a monitor.

Does anyone know what may have caused this? It's pretty disturbing to suddenly not have videos working on a Zoom webinar.