If the content area of an iFrame (embedded video, Agenda page, form, etc.) appears empty when viewing the site securely (using HTTPS), the source link may be insecure.
Check the iFrame's source URL using . Select the widget that contains the iFrame. A Custom HTML widget is the likeliest container, but iFrames may be held in any widget that allows direct editing of HTML. This may include the Editor, Legacy Editor, or Info Advanced widgets.
Check the iFrame's source URL. If it begins with HTTP, then update the URL to use HTTPS. If the iFrame continues to not work with "HTTPS" in the URL, please contact whoever hosts the embedded content for a secure link.