I first noticed this yesterday and from a little research, it looks like the subdomain only started popping up a few days ago on the 22nd. For a while now, if you googled a subreddit, the second result would usually be a beta.reddit.com link to the same subreddit, and it looks like now 110club.reddit.com now pops up sometimes as well. Old.reddit, 110club.reddit, and beta.reddit all seem to be the same thing, hopefully this info helps