Core fails to contact the license portal - You may see this error in the GUI - "String reference not set to an instance of a string" -
Some agent names may be "NULL" in the core console.
open the registry on the core.
navigate to the folder key HKEY_LOCAL_MACHINE\SOFTWARE\AppRecovery\Core\Agents and expand the Agents folder
click on each agent ID in the agents folder, when you do, look to the right window pane. The values will be displayed. The agents that are causing the portal connection to fail will be missing some values.
When you find these entries that are incomplete. you'll need to delete them. Before doing that ensure that you have the IP address or hostname and user and password credentials.