smart:EQ 3 uses the UDP network protocol to share data among different plug-in instances. Therefore, a typical reason for the inter plugin communication error could be that your firewall blocks network connection.
If you are on macOS you need to add an exception for your host in your Security & Privacy Settings. This can be done either manually from the System Preferences or - if you uncheck the "Automatically allow ***" options below - the firewall will prompt you upon the first launch.
After updating the settings please restart your host.