AI Mesh node not found

Hi there,

I have one RT-AC68U (FCC ID: MSQ-RTAC68U), and a never RT-AC68U V2 (FCC ID: MSQ-RTAC68UV2)

The older router is my main router, with a bunch of configuration, including NAT rules and a custom ip range (not using 192.168.x.x).

I've updated the firmware on both to 3.0.0.4.384_21045, and followed instructions on how to reset the newer router to defaults to be able to add it as a mesh node.
I've also connected to 192.168.1.1 and manually set it to be a mesh node.

However, it is...

AI Mesh node not found