Secure Hub shows the following error when trying to connect to Citrix Gateway: "You may need to contact your administrator to verify your sign-on credentials".
Closer inspection of network traffic through Citrix Gateway shows that there is no 'Set-Cookie' response found in the reply to "GET /vpn/index.html"
Working scenario ('Set-Cookie' is present and shows a value for 'pwcount'):
Failing Scenario ('Set-Cookie' is missing and there is no 'pwcount' value found):