On a past webinar we had a panelist share their webcam, but we (organizers, panelists, attendees) could only see a black square/screen for their webcam view. The camera icon next to their name was green to indicate the panelist was sharing a webcam. The panelist could also see their webcam preview in system preferences and in the gallery view with other presenters just fine. They were on a Dell laptop running Windows 10, not connected to VPN. The only way we could resolve it was to have them rejoin the webinar and try sharing webcam again. At first the webcam showed up, but then the panelist stopped sharing webcam for a portion and when they tried to share it again the same issue occurred.
Any reason why the webcam would resort to only showing a black square/screen but they could see their own webcam fine in the platform?