In some cases, you can see a transparent widget in the editor – this is absolutely normal.
Generating a widget preview in a Muse takes a few seconds, while a query to YouTube, Twitch or Vimeo and receiving a response can take more time. In addition, there can be several such requests for one player.
If at the time of the preview generation all the responses from the server are not received and all the scripts are used, a transparent rectangle will be displayed in the editor.
Do not try to fix it, because it’s not a bug.