SSL VPN web portal

Hi all,

We have a problem in customer network. Customer have FortiGate 200D, and when he log in via SSL VPN web portal via Google Chrome or Mozzila Firefox , and then go to "quick connection" and try to open http/https youtube.com for example, he can't play any video.

All other web sites can be opened, but video streams can't. ( picture attached )

If he uses IE or Edge, and then connect to video stream sites, there's no error.

This problem is not isolated only to this customer, we have tested this on 3 different customers and every time there is same problem.

Anybody have idea why and how to resolve this?

Thanks in advance.