This problem has now been resolved. Anyone still experiencing issues connecting to Queen's services with Multi-Factor Authentication should report the issue to the IT Support Centre.
IT Services are currently investigating slowness during Multi-Factor Authentication when user are connecting to Forticlient Campus VPN. User's may experience a 1 - 3 minute delay in receiving the MFA prompt on their device, but the connection will be successful following confirmation. This notice when be updated when additional information is available.