Try /hide_window MainHUD.VideoCapture
IIRC that window isn't really used anymore (I think they got rid of the video capture uploading to youtube thing), but your uisettings probably has an entry for it in there that's causing it to display. Hiding it above might get it to go away, if not you might need to start with fresh UI settings (or /load_uisettings from an alt without it up) or edit your ui settings file directly to hide/remove the window.
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