Chrome Extension for VPN blocked by FortiGate 60E with FortiOS 5.6.2

We are running a Fortigate 60E with firmware 5.6.2. We have a user that occasionally needs to use a VPN (not into our system, but out of our network). We would prefer to use a Chrome Extension that allows turning the VPN access on/off easily. We have tried different extensions but they seem to be unable to get through the firewall. Oddly, if you use a standalone VPN application instead of a Chrome Extension, it works.

Is there something in the application or security policies on the Fortigate that would prevent a VPN via a Chrome Extension?