I have exhausted all possible solutions from the ticket I opened regarding this issue and was told to post here instead.
I have extreme lag, with the Received latency fluctuating wildly. In towns it usually stays in the 3-4 digits while as soon as I get into any kind of instance it spikes into the 4-5 digit range without any rhyme or reason.
I have adjusted my DNS as instructed. I am connected directly to the router by a network cable but cannot set up port forwarding because my current ISP does not allow access to the router configuration. This issue has been ongoing for many months, from Portugal to Poland, even after changing between local internet providers and replacing the motherboard (and the network adapter with it) a couple of months ago.
I have removed the configuration files and tried to run the game with the default settings. I have tried to do a full clean reinstall. I have tried pretty much everything I could and after weeks of troubleshooting attempts the support team told me that they had exhausted all avenues of inquiry and that I should post here. I have no idea what may be causing this and it has never happened with any other game.
I thought the fact that I am playing on a US server from the EU side might be the cause, but after logging in on servers from both sides, Balmung and Fairy, the result was exactly the same.
I have tried to run the game with all browser windows closed and after shutting down any applications that might be downloading in the background. I have uploaded a configuration file to the support team and they did not found anything unusual. I even tried a trial of WTFast (which for those who, like me had never heard of it is supposed to be a type of VPN designed to cut lag for online gaming) and it was only enough to shave off about 20% of the latency according to the readouts, which in the high four digit range means nothing at all.
I do regular malware checks, reset my router and connection countless times. Nothing works. The game gets completely unplayable at the worst parts of it since it's impossible to avoid area attacks that bosses love spamming, so anything I do in terms of endgame or group content ends up being a very frustrating experience on most days.
Just as a point of comparison, I get latency in the 500-800 range just standing idle in Idyllshire.