So someone else tried to figure out what's up with r/8d555938976fc8b four years ago.
People suggested it was an encryption game similar to something else that was going on at the time. I don't think this is the case. It doesn't look like it's intended to be decrypted. All of the posts have since been deleted and there are no comments, well except for one. I dm'ed the account that left that comment and they claim they have no idea what it was.

https://www.reddit.com/r/OutOfTheLoop/comments/4cciq8/what_is_this_encoded_subreddit_about/