Hi Hieon,
We have decommissioned the Seoul location due to recurring problems with the hosting providers, which led to less than acceptable service levels. The quality of the service we provide to our customers is paramount, so based on that we decided we needed to take this server location down. We are looking at other alternatives either in S. Korea or in other locations in the region.
In the meantime, the Tokyo and Hong Kong locations remain a good option to connect to.
Hope this helps,
Davidek