Silent Install of Zabbix Client zabbix_agent2-6.2.6-windows-amd64-openssl.msi, looks like the issue not present in zabbix_agent2-6.0.7-windows-amd64-openssl.msi.

When I set the SERVER property on the silent command line (Command Line: SERVER=aztprdzabbix52.armony.net,dunsupzabpro53.armony.net ServerActive=dunsupzabpro53.armony.net HOSTMETADATA=Windows_Server HOSTNAME=DUN-QAT-S1WINTL HOSTINTERFACE=DUN-QAT-S1WINTL.armony.net) the SERVER is set to 'none' at the end of the installation.

It looks like it's linked to the CustomAction SetServerLocInit which set back SERVER property to none. This custom action is not launched when you're running the installation via the GUI

From the log file

MSI (s) (C4:7C) [16:01:56:314]: Doing action: SetServerLocInit
Action ended 16:01:56: SetWIX_IS_NETFRAMEWORK_40_OR_LATER_INSTALLED. Return value 1.
MSI (s) (C4:7C) [16:01:56:315]: PROPERTY CHANGE: Modifying SERVER property. Its current value is 'aztprdzabbix52.armony.net,dunsupzabpro53.armony.net'. Its new value: 'none'.