The 11.1.x Endpoint agent has been installed with an uninstall password key using the UNINSTALLPASSWORDKEY= parameter
You try to upgrade to 11.6.x or 12.0 with or without a new UNINSTALLPASSWORDKEY= parameter (if this parameter isn't specified the uninstall password key isn't changed during the upgrade)
The upgrade stops the EDPA service but does not complete the upgrade
Upgrading to 11.5 with or without a new UNINSTALLPASSWORDKEY= parameter succeeds
If the installer is run in quiet mode with the /q switch you see no errors
If the installer is run without the /q switch you may be prompted for the uninstall password but even if you enter the correct password (the password used to create the uninstallpasswordkey for the 11.1 agent installation) the installation still does not complete or display any further errors
As a workaround first uninstall the 11.1.x Endpoint Agent then install rather than upgrade the 11.6.x or 12.0 Endpoint Agent
Alternatively you can upgrade from 11.1 > 11.5 > 11.6 or 12.0