I have marked the other thread as resolved, because ipv6 is up and running on my home network.
This is a new/different issue and I've not been able to find any similar threads.
All the subnet addresses are being automatically updated when the new /48 block is received from the ISP, but the network hosts (e.g. my Windows PC) aren't updating their ipv6 addresses unless I manually reconnect the device by disabling and then enabling the LAN port.
Perhaps this is more of a Windows issue, but maybe there is an OpenWrt fix?