In a scenario where HA is enabled in the VCO but the HA status remains at "pending standby detect" a software upgrade may fail, and you might encounter the following error:
Error: "Failed to apply new configuration for imageUpdate version."
Active unit considered that standby device failed to upgrade, although there is no Standby Device connected.
To upgrade the device, disable the HA configuration in the VCO. Once the upgrade is complete, you can re-enable HA.