[AC68U] using IPv6 on LAN

Hi there.
I’ve been having issues getting some Nest Protects onto my network. Nest support are out of ideas, but I suspect the issue is because they need to use IPv6.

I’ve just done a factory reset of my AC68U, and set it to use a native IPv6 WAN connection, and stateful LAN.

However my device list is full of devices with IPv4 addresses (and the Protects aren’t connecting).

Is there something else I need to set to use IPv6 for my LAN?