Hi Merlin,
I had been testing out your firmware from RT-N66U_3.0.0.4_374.34_2.trx to RT-N66U_3.0.0.4_378.50_0.trx.
Apparently, only the firmware 374.34_2 or earlier allows me to use ipv6 without problem.
Any firmware after 374.34_2 till today, 378.50_0, I am not able to get ipv6...