I want to add a couple of good ones I’ve found:
Jeff the Killer lost media: no one knows where the original Jeff The Killer image came from.
Mortis.com: old weird website
Also here’s a good website on various obscure computer/Internet related oddities: https://suricrasia.online/iceberg/
Almost all the “internet mysteries” I hear of turn out to be overblown normal things, such as that Cicada 1138 thing which turned out to be not an agency recruiting tool but a band gimmick, or that missing Nova Scotia guy who had been known for years but whose identity was ignored to keep the vibes going. The closest things to what you’re asking would be stuff like what you’d find on r/TOMT.
It’s Cicada 3301 and I have no idea where you heard the “band gimmick” thing but it’s just not true. I mean… It doesn’t even make any sense. If it was a gimmick to get a band popular then it did an insanely bad job at doing so after multiple puzzles across multiple years and swearing the winners to privacy.
Was trying to say Cicada 3301 went nowhere. It’s been a decade. The puzzle gave no assurance that it wasn’t some amateur thing to start out with, and there was a TopTenz video that showed the end of the clue hunting puzzles was simply some obscure musical band making a game with no other prize than front row seats to a personal performance.
Another example of overblownness, if we may call it that, is the CIA’s supposed Kryptos statue. Or the Gravity Falls puzzle. When was the last time you heard a puzzle actually culminate or clarify the “race” ended? How do people think cults work?
I cannot find a single credible source for the band thing. There is a band called Cicada 3301 but they are completely unrelated. They named themselves after it but do not have any connection or affiliation. I wouldn’t exactly use a Top 10 video as a reputable source.
As for Kryptos, it’s a world famous and unsolved bit of cryptography. If it’s overblown then solve it?