This is a result of a bug on our side that we are fixing right now.
You are missing data-widget-id. Usually this will be available in the code you copied, but because of a bug on our side that is missing in the code snippet.
You can fix it by finding the widget id (go to the widget in https://twitter.com/settings/widgets) and find the widget id in the url (a large number). Then add the id into data-widget-id="" in the code snippet.
Sorry about the inconvenience.
Edit: Fixed url widget -> widgets