Forticlient keeps re-authenticating, causing unexpected 2FA prompts

We have Forticlient (5.4.1) configured for SSL VPNs back to our Fortigate (5.4.1).  It uses a RADIUS server that is tied to Duo Security for Two Factor.  Everything works, but we are experiencing an issue.

Forticlient keeps re-authenticating after the initial connection, and this triggers a 2FA push that is often missed by the user, which disconnects the VPN. 

Is there a way to prevent this behavior?  It's not Duo.  This does not happen with our legacy Firewall VPN solution.

Thx!