Updated to the new version 378.50 on RT-AC66U and lost all ability for IPV6 access. Reverted back to the previous beta 2 version and IPV6 returned.
It doesn't kill it. You need to hit "apply" several times when activating IPv6; sometimes rebooting the router after implementing it will cause it to once again show your IPv6 address in the GUI. I've used many different versions of Merlin's FW, and occasionally it looked as though they were killing IPv6. Turned out not to be the case, and it was just a question of either rebooting the router or logging out and then logging back into the GUI again.
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