Hi,
no always WAN port. LAN port is only for your internal network - so your clients or any other devices. I don't know Virgin, so I am not completely sure what you need to do now.
There are some known compatibility issues with the 2.5 Gbps port of the Flint2 and other devices. If you know how to SSH into your Flint, you can force it to be 1 Gbps - which might solve this issue.
If you don't know how to do so, let me know!