I have a user attempting to log in, and they're using an IP address that's not banned, and they're getting a reason "Sorry, Guest" that says they're permanently banned. I have no idea which ban triggers caused them to receive cookies or local storage to mark them as permanently banned only on one computer. How do I diagnose this?
Well, when you create a ban you have the option to include a description of the reason for the ban and a custom message to show to the banned users, so probably it would be good practice to fill it. :P
That said, if the fields were not filled, I think it should be possible to output the id of the ban as informative measure for the user to report to the admin.
Turns out it was someone setting rather generous masks on server hosts that would be responsible for VPN services, rather than reporting abusive users to the provider itself, and the new user was still connected to their VPN when they tried to use the forum.