I wonder how that algorithm works. At the risk of discussing a bit of a taboo topic (are there rules against this? there might be...), I've never vouched for a comment and had it come alive. I have many times been the final nail in a comment where my flag caused it to die, but I have never seen the opposite with vouch.

You are probably shadowbanned from flagging and vouching, which is separate from a commenting and posting shadowban. A shadowbanned comment only requires one vouch to come alive. A comment that is dead because of excessive flags or moderator action may require more.

Interesting. Every time I've ever vouched a comment, it came alive. (Though the last one I vouched ended up dead again after enough people flagged it, oops. I hope that doesn't mean I lost my power. In my defense, it was flagged to death based on being AI [apparently], which I didn't pick up the signal on, nothing super terrible / controversial.)