I, surprisingly, got a quick response to my support ticket via email.

The technician suggested Microsoft Edge might be the culprit (it wasn't) and had me make sure some settings were correct there. They also asked me to set FFXIV to run as administrator to see if that helped (it did not). Finally, they asked me to forward some ports on my router (this also did not help). Their final suggestion was to go directly through the modem, which I cannot do as my router is a modem/router combo.

Failing those, the technician also suggested changing world/data centers, but seeing as how it's affecting all of us across multiple centers, I did not try that.

I did respond with my trace log, pointed them to this thread and their own tweet, and asked if the issue could be escalated. I got the feeling the technician assumed the problem was specific to me and is not aware that it is affecting a larger amount of people. If I get an update, I'll let you know.