The fact that your router sees the device rules out a bunch of things. Most of the time if the device manages to start its network it also starts the services that allow it to be discovered by Buffalo's tools. The fact that the web interface isn't showing up would indicate that there's an issue with the device or some network issue preventing you form getting to it.
The communication protocol used by NasNavigator/Lsupdater/etc hasn't really changed over the years. Folks use the current version with even older devices, so i don't think that's the actual issue.
Some network configurations can block this communication but it is uncommon. Specifically, they communicate using UDP broadcast packets. One thing to check is whether the firewall on your PC is stopping NasNavigator from sending those packets. It is also possible that your router does not forward those packets for some reason. "Mesh" networks typically don't forward them from one access point to another, they also typically aren't forwarded across VLANs. Some wireless routers have options to isolate wireless clients from each other which would also block that type of packet.