Well the ban list is stored in tables in the database.
There is a separate one for email,host(ip) and users.
They all begin with banned.
So the only way to restore what you had is to login to your cpanel and use something like phpmyadmin and take a peek.
Possibly they need a repair or if you have a db backup you can restore just those three tables.
FYI,
If they got wiped I would suspect the whole database need to be checked.
