I've installed the agent on the server itself. In the log it shows "IpDiscover ignored". The agent discovers only the itself. I have configured snmp on other servers in the same network (172.16.121.0/24) and SNMPWALK shows it can connect. 
How do I force the Discovery? 
In Network -> Administer I've added the Subnet (172.16.121.0/24) and Communities.
In Group name -> Select a parameter to be modified -> Network scan: I do not see the Network I added in the option. See picture one. 

But in All Computers -> Computer -> Configuration -> EDIT -> Network scans -> IPDISCOVER  -> I can see the Network and I've selected it. See picture two.
Note: I added the new test_group to the self discovered host (the ocs server) by All Computers -> Computer -> Configuration -> "Statically add this group".

Here is the log:
Thu Apr  9 15:38:53 2020][debug] Ocsinventory unified agent for UNIX, Linux and MacOSX 2.0.5
[Thu Apr  9 15:38:53 2020][debug] Log system initialised (File)
[Thu Apr  9 15:38:53 2020][debug] --scan-homedirs missing. Don't scan user directories
[Thu Apr  9 15:38:53 2020][debug] Accountinfo file: /var/lib/ocsinventory-agent/https:__test.doimain_ocsinventory/ocsinv.adm
[Thu Apr  9 15:38:53 2020][debug] OCS Agent initialised
[Thu Apr  9 15:38:53 2020][debug] Turns hooks on for /etc/ocsinventory/modules.conf
[Thu Apr  9 15:38:53 2020][debug] Ocsinventory unified agent for UNIX, Linux and MacOSX 2.0.5
[Thu Apr  9 15:38:53 2020][debug] Log system initialised (File)
[Thu Apr  9 15:38:53 2020][debug] Calling handlers : `start_handler'
[Thu Apr  9 15:38:53 2020][debug] [download] Calling download_start_handler
[Thu Apr  9 15:38:53 2020][debug]  - Net::SSLeay qw(die_now die_if_ssl_error) loaded
[Thu Apr  9 15:38:53 2020][debug] Compress::Zlib is available.
[Thu Apr  9 15:38:53 2020][debug] Calling handlers : `prolog_writer'
[Thu Apr  9 15:38:53 2020][debug] sending XML
[Thu Apr  9 15:38:53 2020][debug] sending: <?xml version="1.0" encoding="UTF-8"?>
<REPLY>
  <OPTION>
    <NAME>IPDISCOVER</NAME>
    <PARAM IPDISC_LAT="100">172.16.121.0</PARAM>
  </OPTION>
  <OPTION>
    <PARAM TYPE="CONF" PERIOD_LATENCY="1" TIMEOUT="30" PERIOD_LENGTH="10" CYCLE_LATENCY="60" FRAG_LATENCY="10" ON="0" EXECUTION_TIMEOUT="120" />
    <NAME>DOWNLOAD</NAME>
  </OPTION>
  <OPTION>
    <NAME>SNMP</NAME>
    <PARAM TYPE="NETWORK" SUBNET="172.16.121.0/24" />
    <PARAM AUTHPASSWD="" TYPE="COMMUNITY" NAME="TestCommunityString" VERSION="1" USERNAME="" AUTHKEY="" />
    <PARAM AUTHKEY="" USERNAME="" VERSION="2" TYPE="COMMUNITY" NAME="TestCommunityString" AUTHPASSWD="" />
    <PARAM AUTHKEY="" USERNAME="" VERSION="3" AUTHPASSWD="" TYPE="COMMUNITY" NAME="TestCommunityString" />
    <PARAM NAME="TestCommunityString" TYPE="COMMUNITY" AUTHPASSWD="" VERSION="2c" USERNAME="" AUTHKEY="" />
  </OPTION>
  <INVENTORY_ON_STARTUP>1</INVENTORY_ON_STARTUP>
  <PROLOG_FREQ>1</PROLOG_FREQ>
  <RESPONSE>SEND</RESPONSE>
</REPLY>
[Thu Apr  9 15:38:53 2020][debug] [download] Writing config file.
[Thu Apr  9 15:38:53 2020][info] [download] Download is off.
[Thu Apr  9 15:38:53 2020][debug] Ocsinventory::Agent::Backend::IpDiscover::IpDiscover ignored
[Thu Apr  9 15:38:53 2020][debug]  - nmap found
[Thu Apr  9 15:38:53 2020][debug] Ocsinventory::Agent::Backend::IpDiscover::Nmap ignored
[Thu Apr  9 15:38:53 2020][debug] Ocsinventory::Agent::Backend::OS::AIX ignored
[Thu Apr  9 15:38:53 2020][debug] Ocsinventory::Agent::Backend::OS::BSD ignored
..........................
log removed.
[Thu Apr  9 15:38:53 2020][debug] Calling handlers : `inventory_handler'
[Thu Apr  9 15:38:53 2020][debug] [download] Calling download_inventory_handler
[Thu Apr  9 15:38:53 2020][debug] Section HARDWARE has changed since last inventory
[Thu Apr  9 15:38:54 2020][debug] sending XML
[Thu Apr  9 15:38:54 2020][debug] sending: <?xml version="1.0" encoding="UTF-8"?>
<REQUEST>
  <CONTENT>
    <ACCOUNTINFO>
      <KEYNAME>TAG</KEYNAME>
      <KEYVALUE>NA</KEYVALUE>
    </ACCOUNTINFO>
    <BIOS>
      <ASSETTAG>No Asset Tag</ASSETTAG>
      <BDATE>12/12/2018</BDATE>
      <BMANUFACTURER>Phoenix Technologies LTD</BMANUFACTURER>
      <BVERSION>6.00</BVERSION>
      <MMANUFACTURER>Intel Corporation</MMANUFACTURER>
      <MMODEL>440BX Desktop Reference Platform</MMODEL>
      <MSN>None</MSN>
      <SMANUFACTURER>VMware, Inc.</SMANUFACTURER>
      <SMODEL>VMware Virtual Platform</SMODEL>
      <SSN>VMware-42 37 9f 16 5e 35 e9 ed-8c df da 6b f5 db cb 1a</SSN>
    </BIOS>
    <CONTROLLERS>
      <DRIVER>agpgart</DRIVER>
..........................
log removed.
  
    <VIDEOS>
      <CHIPSET>VGA compatible controller</CHIPSET>
      <MEMORY></MEMORY>
      <NAME>VMware SVGA II Adapter</NAME>
      <RESOLUTION></RESOLUTION>
    </VIDEOS>
  </CONTENT>
  <DEVICEID>ocs-2020-04-09-12-16-35</DEVICEID>
  <QUERY>INVENTORY</QUERY>
</REQUEST>
[Thu Apr  9 15:38:54 2020][debug] =BEGIN=SERVER RET======
[Thu Apr  9 15:38:54 2020][debug] $VAR1 = '<?xml version=\'1.0\' encoding=\'UTF-8\'?>
<REPLY>
  <RESPONSE>NO_ACCOUNT_UPDATE</RESPONSE>
</REPLY>
';
[Thu Apr  9 15:38:54 2020][debug] =END=SERVER RET======
[Thu Apr  9 15:38:54 2020][debug] Calling handlers : `end_handler'
[Thu Apr  9 15:38:54 2020][debug] [download] Calling download_end_handler
[Thu Apr  9 15:38:54 2020][info] [download] Beginning work. I am 24528.
[Thu Apr  9 15:38:54 2020][info] [download] Option turned off. Exiting.
[Thu Apr  9 15:38:54 2020][debug] [download] End of work...