Notifications are being created for internal admins
If notification audience is 'admin', the notification gets created for all admin accounts including internal anonymous and api admins. They won't be removed or read. The code that should be fixed is here https://github.com/theforeman/foreman/blob/1.15-stable/app/models/notification.rb#L47 it should probably add condition
where.not(:login => [User::ANONYMOUS_ADMIN, User::ANONYMOUS_API_ADMIN])
EDIT: or simply add the scope "except_hidden"