I regularly "report" behaving shadowbanned people. If someone has gone a while only saying productive things, the system unbans them.
On the other hand, I'm surprised how profilic certain people are. They get absolutely no feedback, but will go around trolling people several times a day.
We have to unban accounts manually, though users of course can still vouch for their comments in the meantime, which is basically a per-post unban mechanism.
If anyone notices an account that is banned that shouldn't be banned, they're welcome to let us know at [email protected]. We don't want anyone to be banned if they've fixed whatever the original issue was and are abiding by the site guidelines (https://news.ycombinator.com/newsguidelines.html).
On the other hand, I'm surprised how profilic certain people are. They get absolutely no feedback, but will go around trolling people several times a day.