Throwing my hat into the ring that I too am experiencing this problem. I've been through every suggested check on the support articles, have even contacted my ISP just to make sure they aren't restricting the ports that FF14 uses or anything that could otherwise cause this.

FF14 is the only game/internet service I have which experiences this problem. Some days I can play for many hours and not have a single 90002 error. Other days I'll experience one or two of these errors. Then on some I'll spend up to three hours repeatedly disconnecting, at intervals anywhere from 10seconds to 10minutes, before the issue stops as suddenly as it began.

For a matter of interest there are two other people in my FC that also experience this issue, both in different countries from me and from each other.