[HECnet] Off Topic - pfSense on Hyper-V

I realise this is completely off topic, but I think this list has a lot of experienced networking people, so I am hoping someone might have a suggestion. I have pfSense running as my firewall at home, running on Hyper-V. In case you don't know, it runs on FreeBSD. I have run it for a few years and really want to get it upgraded to the latest. But when I do the upgrade doesn't work because every packet in the WAN interface seems to get lost, it just cannot send anything to the WAN. The LAN side is fine. I posted on the pfSense forums about this a long time ago. I got some questions about the MTU, but it was fine I was just wondering if you have any thoughts/suggestions/experiences? Thanks Rob