Assuming no violent (as in promoting) or particularly racist/sexist comments in their history, this hits some new accounts if they're using a VPN (some particular VPNs, I guess?). Sometimes they get caught up in the same filters used to block spammers/abusers from using HN. Or if their first (or one of their first) comments was a link without substantial text, that also gets people put into some kind of "spammer" category. You, or they if you tell them, can reach out through the email in the contact link at the bottom to get the ban addressed.