Have you ever encountered such a situation (e.g., Reddit, or even HN)?
N.B. The staggeringly elaborate Cicada 3301 puzzle [1][2] does require deciphering steganographic messages, but they aren't posted in public channels.
[1] https://www.youtube.com/watch?v=RatbYqc0-jE
[2] https://uncovering-cicada.fandom.com/wiki/Uncovering_Cicada_Wiki