The Agent's install request pointed at http://cn.patch.battle.net:1119/<product>.
That host only 301-redirects to the country's version service today; Blizzard's
China client asks cn.patch.battlenet.com.cn:1119 directly.
The update check built <branch>.version.battle.net, so a China install (branch
cn) asked cn.version.battle.net, which does not answer; the China service is
cn.version.battlenet.com.cn.
Only region cn changes.