Multiple WAN but only 1 WAN is able to access at the same time

Currently I have 2 WAN link for my new Fortigate 60E

WAN 1 --> PPPOE with fix IP

WAN 2 --> Fix IP 

While both is connected, WAN2 unable to connect to VPN and cannot access via fix ip from WAN, The VPN only show connected and I can access the WAN2 public IP from WAN while WAN1 is disconnected. I already check the both WAN setting and routing are the same. Is that anything wrong on my setting?