What was your previous configuration and what was the reason for changing it since it was working fine?
Try to flash RMerlin's 374.43 firmware on your AC66R if you aren't using it already.
Quite complicated
As first, I was was connecting Dlink directly to Asus ( DLink LAN to Asus Internet Port)
But I didnt change any configuration, everything was default except the standard wifi configuration.
Everything was fine, until lately startup to connect fibre took half an hour or more which was weird.
Call Starhub , Techician came down and say I connected wrongly... he connected lan to lan.(Which kinda ******** since the configuration was done when the fibre first startup) Everything was fine
Problem is because I using trying to use Astrill VPN on Asus, with this configuration by Starhub. I wont be able to use Astrill VPN from what I tested.
*I cant use ONT also as my family using Digital Voice, have to use DLINK.
Thats why the configuration was set as per TS advice. Now Astrill VPN working , only the random disconnection. Which is weird... sometimes happen in few hours. Sometimes wont.
And as I mentioned, I can even play DOTA while the net is down. ( Net down as in unable to surf net via WIFI , LAN ( All house computer))