I have also been having connection issues since September 19th. It happens regardless of what I am doing in game. The red disconnect symbol will appear next to my name. Sometimes it goes away on its own, other times I get disconnected with a 90006 error. I am usually able to log back in immediately, but the issue has been ongoing regardless of the time of day.

Similar to Thighdaelyn, my connection is wired and has not changed. All of my router/anti-virus/etc settings have not changed. All other online games and services that I have used recently have worked just fine and the FFXIV disconnects that I have experienced never interrupt any other internet games or services that I have been using at the same time.

I can only wonder if this has something to do with the Typhoon that hit Japan on the 19th and 20th, but then I am left to wonder why that would affect the NA servers.