Strange FortiClient Behaviour, SSL VPN not working with Domain PCs

Hi there,

I'm experiencing this strange issue with a customer, where SSL VPN works flawlessly for any PC not connected to the client's local Active Directory Domain, but any corporate laptop connected to the Domain cannot pass any traffic. Same username and policies can be used on a non-domain PC, and the traffic works, but on a Domain PC it doesn't send traffic. I've never seen this type of issue before...