Acabo de recargar la página y comprobar la lista de errores de la consola. Misteriosamente, en cuanto he accedido a uno de los enlaces de error, el juego me ha empezado a funcionar.
Te dejo la traza por si quieres depurarlo.
Autoplay is only allowed when approved by the user, the site is activated by the user, or media is muted. index.html
HTTP load failed with status 403. Load of media resource https://v6p9d9t4.ssl.hwcdn.net/html/1746228/audio/click.mp3 failed. index.html
HTTP load failed with status 403. Load of media resource https://v6p9d9t4.ssl.hwcdn.net/html/1746228/audio/darkshadow.mp3 failed. index.html
NotSupportedError: The media resource indicated by the src attribute or assigned media provider object was not suitable. behavior.js:234
NotSupportedError: The media resource indicated by the src attribute or assigned media provider object was not suitable. behavior.js:234