Some messages are prevented from posting because they include Markdown headers or hyperlink formatting.
I don't know how the rule works but it sometimes prevents other messages, like this code snippet I tried to post.
Discord now has other methods to prevent abuse of the markdown link hiding issue, it has an extra pop-up to prevent users accidentally opening links and tells them exactly where they are going.
As for markdown headers... idk maybe the rule can be revised to not seek inside code-blocks across newlines somehow

it doesn't even allow lookaheads


