When does an IP get blocked?

We have used open source version of discourse for a community with 200K users.

All our user registrations are done via remote service. Which means all the users have the same registration IP. We have set the max registrations per IP value also to be high (9999999)

Over the weekend, we realized that all new registrations are getting blocked with the error “ServiceError: New registrations are not allowed from your IP address”

We were able to unblock the IP by removing the entry from “screened_ip_addresses” table. However, want to understand why was the IP blocked?

Can anyone help me understand under what circumstances does discourse block an IP? Is this something that an admin could have accidentally done?

When an admin deletes a user there is an option to block the IP addresses of the user (both the registration IP and last IP). Maybe a user was recently deleted by an admin and the admin chose to block the IP address? This is the only way that I’m aware of where discourse blocks an IP address. You can review the staff actions logs to see if a user was deleted and had their IPs blocked.