Okay, so I've been 90002-free for about a week now, after my last "success" stopped working the next day.

I had tried:
- Forwarding the appropriate ports on my router
- Updating everything I could find
- Changing the recommended I.E. settings
- Running via a VPN, having it route me to Houston just in case the blockage was somewhere in the bay area
- Reinstalling the game

Then I tried turning off Windows Defender, and discovered that... it wasn't running. It wasn't even working! I couldn't boot it up at all! Attempting to update it just led me to errors. I figured that it was probably some virus I picked up at some point, so I ended up completely wiping my computer and reinstalling my OS, in the process upgrading from Windows 7 to Windows 10.

First thing I did after booting up my new OS was install FFXIV and log in. I was disconnected within 20 minutes just standing around Gridania. I wasn't even moving, just fixing my UI. Double-checked that all the IE settings were still at their recommended positions, but it didn't help. Every time I logged in, I couldn't stay connected for long at all.

Tried running my VPN (Windscribe; I've got a lifetime pro account), and got the same. Tried running the VPN but turning off its Firewall, still disconnecting. Tried turning its firewall on but turning OFF Windows Firewall, and this finally seemed to work.

Ran the game idle for hours that day with not a single disconnect. Have been running dungeons and raids since with zero issues.

One day, I forgot to turn on my VPN, but Windows Firewall was still turned off, and I got a 90002 in the middle of crafting something, not long after logging in u_u Switched my VPN back on and again, no disconnects at all.


So TL;DR: it was only the combination of BOTH of these two things that fixed the problem:
- Turning off Windows 10 built-in Firewall
- Routing my traffic through a VPN

Hope this is helpful to someone.