https://www.reddit.com/r/ffxiv/comme...ting_game_504/

Well this solved my issue with absolutely no thanks to official SE support, who recommended I contact my ISP.

There are circumstances where your config files will be corrupted. These config files are in a separate location compared to the game files, so uninstalling and reinstalling the game will not fix this. You will have to redo all of your UI/HUD settings if you whack the whole folder (like I did)