The issue occurs when you attempt to download the PAC file from ThreatPulse by entering the URL (https://portal.threatpulse.com/pac) on the browser address bar. The returned PAC file contains a line with the following error:
The IP provided here does not always reflect the IP address of the discovered data pod discover.
You are unable download the PAC file correctly if not explicitly connected to Web Security Service.
To be able to download the PAC file by entering the https://portal.threatpulse.com/pac URL in the browser, you must remove the browser "Automatic configuration scripts" settings in settings.
IE:
Menu > Internet Options > Connections > LAN Settings > User automatic configuration file.
Firefox:
Menu > Tools > Options > Advanced > Network > Connections Settings > Automatic proxy configuration URL.