I'd love to know why Duos doesn't work in any of the Asian servers. Do people just not play them? Or is there a fault in your system?
We are not aware of any problems with matchmaking on Asian servers, but we do see fluxations of player counts on certain playlists for each region. Currently, Trios is our number one played mode, followed by ranked, so that does mean that you may see fewer people playing Duos in off-peak hours and queue times could go up. You can try changing to another datacenter thought!