I haven’t been able to find the court orders for any of the website blocks (only newspapers talking about it) but it’s all related to an order of the Constitutional Court that prohibits basically anything that promotes the referendum since it’s against the Constitution.

E.g. http://www.elmundo.es/cataluna/2017/09/23/59c69496468aeb8c7f... https://www.elindependiente.com/politica/2017/09/25/la-guard...