Disable the SHub's Firewall and flood detection. You are still behind NAT so you are not compromising your network. If you are still unhappy get a free software firewall.
Reboot SHub and see what you've got.
I haven't got a Buffalo NAS so can't check for you.
I remember I had a bit of a performance setting up my own NAS IIRC a pinhole reset was required to access it and setting it to a static IP solved the issue for me.