Despite being live for around five years now, the fan remake of Club Penguin, Club Penguin Rewritten has officially been taken offline. The URL for the game now takes you directly to a notice from the City of London Police, and as for why this is the case, it's noted in the official Discord for the game that it was due to a "full request" stemming from a copyright investigation by Disney.
The game has been operating without much of an issue from Disney for a while now, albeit if it, like other Club Penguin clones, has had its own array of problems regarding very explicit language that is left mostly unregulated in-game.
There has yet to be an official announcement from Disney about Club Penguin Rewritten and why it is being taken down, and likewise we're awaiting a report from the police about their investigation on the matter.
Thanks, GamesRadar.