==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.3
- Deployed with iRedMail Easy or the downloadable installer? downloadable installer
- Linux/BSD distribution name and version: Debian 9
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): LDAP
- Web server (Apache or Nginx): nginx
- Manage mail accounts with iRedAdmin-Pro? Yes
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

In the template templates/default/dashboard.html it literally says N/A:

<tr>
 86                     <td><i class="fa fa-ban fa-lg color-red"></i></td>
 87                     <th>{{ _('Banned IP Addresses') }}</th>
 88                     <td class="full"><a id="count_banned_ip" href="{{ ctx.homepath }}/activities/fail2ban/banned">N/A</a></td>
 89                 </tr>

Was this an oversight? Surely you could ask SQL to count the rows in the DB.