IPv6 and Thread Border Routers

Recently setup a thread mesh network using Alexa echo 4th gen for thread border routers. I use an Araknis AN-310 router. To the best of my limited ability, I've enabled IPv6 in the router choosing "Dual-Stack IP (IPv4 and IPv6)". Additional LAN settings are unknown as Cox online support has not proved helpful. 

1. IPv6 address? I've chosen the IPv6 default gateway that displays for my wireless LAN adapter
2. Prefix length? I've entered 64

I'm successfully able to add devices to the thread network. However, within a day or so, the thread border router can no longer communicate with the thread devices. After useless attempts to delete and readd devices, the same annoying disconnect is experienced in the next day or so.

Anyone out there successfully setup a thread mesh using Cox "Dual-Stack IP (IPv4 and IPv6)"?