I realize that this is resurrecting a dead topic; however, since the best solution here was "uninstall; reinstall" I thought I'd add what my client's issue was to potentially save you time and googling purposes.
Client had downloaded latest VPN client version (6.2 something in my case, as of this posting) onto her machine. Tried to connect to Foritgate VPN gateway, which resulted in client experiencing "Connecting" but never completing the VPN connection. Connecting to the VPN failed. Traffic sniff on the gateway indicated client never even initiating a connection.
Solution was to upgrade her MacOS. MacOS was version 10.11, minimum required 10.12. Client upgraded to 10.15, and Forticlient VPN software worked as expected.
The reason I post this, is because I just made the assumption her OS was up to date and met requirements, and I wasted a bit of time troubleshooting the issue because of this over sight.
tl;dr Check your MacOS version and make sure it's up to date.