The issue has been resolved and the Signature ID 14191 was removed from the X-VPN Application list.
To verify, go to MANAGE | Rules | App Control and ensure the App Signature Database Timestamp shows UTC 05/09/2019 04:51:29.000 or later. Otherwise click UPDATE button next to the DB Timestamp to trigger Database synchronization.
The issue was reported to the respective Team and a solution is being worked on.
NOTE:The issue affects only customers who are blockingX-VPN Application in Proxy-Access Category of App Control
Verify if the website is blocked due to the "App Control PROXY-ACCESS signature: X-VPN -- HTTP Activity 2, SID: 14191, AppID: 2083, CatID: 27" by checking the affected website IP under INVESTIGATE | Log Events
Temporarily disable the signature by setting Block: "Disable" and verify if access is restored.