"It appears that the voidnull account has been disabled on Hacker News."
I think they ban tor, or new-account tor users (which completely defeats the purpose of using tor in the first place).
I created my account and log in through Tor and don't experience any problems. I don't think I ever logged in outside of Tor, but I don't consider it to be a security requirement and am not sensitive about it, so it's possible there are exception (in particular it's that I misremember creating the account through Tor).