Spotlight failed during screenshare

We had a few meetings with 20 attendees. We spotlit the main speaker in each meeting so that we would only see the speaker, and not the attendees--we didn't want attendees to appear in the recording when they asked questions. We only wanted the speaker to appear in the recording.

This seemed to work for most of the 75 minutes of the meetings. But when I watched the whole recordings, I saw that a few times, even though only the speaker was spotlit, an attendee appeared in the spotlight window when they asked a question. Again, this didn't happen every time--it was random--but it only happened when the spotlit speaker was sharing their screen. Sometimes during screenshare the spotlight worked, sometimes during screenshare it failed.

What happened and how can we prevent this?

Thanks!