They didn’t fix it.
Back in July, after this had already been on-going for a couple of months, the Community Manager made this thread to ask for data from players…
The Community Manager said…
That was over a month ago, and he hasn’t posted on the subject since.
From my own experience, and lots of responses in that thread, it seems to be mostly affecting players who are Immortals. This was certainly the case for me, with exactly the same symptoms as you’re describing (i.e. slow zone-in to Vault, dungeons, raids, teleporting between zones, and so on) that simply went away when I went back to being a Shadow a couple of weeks ago.