AC68U running Beta5...
UPnP with multiple console issue looks resolved. 1 XB One, 2 XB360s and 1 PS4 have open nat at the same time.
For XB One owners...
Had an issue with IPv6 after flashing Beta5 from 4 (and clearing nvram). The readiness test at
www.test-ipv6.com returned 7/10 and showed that my IPv6 connection appeared to be using Teredo. Nothing showed up for WAN IPv6 Address in the System Log. I also noticed in the Port Forwarding log that 2 IP addresses were associated to my XB1 (pior IP & new IP), and description was "Teredo" for both. So I power-shutdown the XB1 and reset the router, re-activated IPv6 and ensured that it was working. Then I turned on the XB1 and checked everything again: IPv6, UPnP/Open NAT for all consoles, etc. -> all OK
To power shutdown the XB1, while on, press and hold the Xbox button on the front of the console for approximately 10 seconds.