FFXIV Launcher Error Unable to Download Patch Files

[Seitheach]

I've been having the same issue over the last week and a bit (can't recall if I first noticed it when trying to update for the first time after 5.1 or the first mini update afterwards). In Perth, Australia on the iiNet (TPG) network.

Within a few seconds of beginning the patch it failed with:
FFXIV Launcher Error
Unable to download patch files.
[30413][25008][20495][20495]

Ultimately I was able to solve it by changing DNS locally on my computer (and then flushing DNS to make sure it kicked in). Note that Google DNS (8.8.8.8 / 8.8.4.4) did NOT work. I had to try a third one (Open DNS 208.67.222.222 / 208.67.220.220) before it worked. Going back to my ISP standard DNS after updating allows me to play as normal.

Prior to that I went through the whole rigmarole
- Google IPV4 and IPV6 DNS.
- Investigating file access permissions for My Documents > Final Fantasy file.
- Making sure there were no user access permission issues.
- Disabling Windows Defender firewalls and uninstalling my AV completely.
- Swapping to the original launcher.
- Uninstalling the client and game completely - this got it patching again for a good 20GB, but it still failed with the same error after a certain point (and restarting client then gave the same error after a few seconds).

Seems like there -might- be some kind of routing issue for certain files in the patch - are you also on the iiNet / TPG network? If it is an ISP issue the same thing's likely to happen next patch.

I would like to run some more extensive ping / traceroutes on my ISP's DNS vs OpenDNS's one and ask my ISP to review, does anyone know if I should just use the remote IP Windows Resource Manager uses or is there a known list for FF14 servers?