Webinar Attendees Using iPads Have No Video

For the weekly Zoom webinar that we have, some attendees using iPads see no video of the webinar but have the audio. They enter the webinar by using the attendee link that we send them. Once they enter, they see a black screen, the Zoom menu, and hear the audio. The problem didn't occur earlier in the year but has appeared in the last two months. Any ideas of the cause and how to resolve?