Tom's lost my original post when it asked me to login, so rather than re-writing it all again, here's the condensed version:
Any ideas how to solve this problem?
Bought a new ASUS RT-AC86U router.
Unable to do anything on the NAS that requires it's IP address (i.e logging in to the NAS, connecting to Deluge)
Still able to access shared folders on it via Windows Explorer
Pinging the NAS gives me a bunch of letters and number starting with "fe80::". Google says this is an ipv6 address, so I disabled ipv6 on my router, but this didn't change anything.
Any ideas how to solve this problem?