It's usually not an algorithm glitch, but an intentional technique by content creators. Videos with encrypted text are often used to avoid automatic filtering - when the TikTok algorithm blocks or reduces visibility of content with certain words or phrases. For example, if it's about politics, health, money schemes, or other sensitive topics, creators encrypt the text so the content doesn't get flagged by the system. Sometimes it's also done for artistic effect - just as an unusual format that stands out in the feed.
Deciphering such text is usually pretty straightforward. If it's a simple letter substitution (like all "a"s replaced with "@", or letters just rearranged), you can try to guess based on the video's context or switch to an English keyboard layout - sometimes you need specific symbols. If the cipher is more complex, a text analysis app or just plain trial and error in your head can help. But often the creator themselves leaves a hint or the solution in the comments, because the whole point of the video is for people to actually watch it and share it.