XenForo_Helper_Media::_convertMediaLinkToEmbedHtml blindly attempts to convert any text into a media bbcode. This causes ridiculously long execution times if there are a lot of media sites added, and dealing with +20kb of text. An 2kb length limit is the practical limit to ensure IE compatibility, while most servers max out at 8kb. The media editor appears to sometimes do this for some people. ie the URL; index.php?editor/media where they paste an entire image (as data:image/jpeg;base64,...) into the URL textbox.