I submitted this as a ticket, ref #90022524 on the EU Support (my main account is on EU) and they advised they couldn’t do anything about it so I should submit a bug report here.
I am able to log in to the EU forums, and my EU support, however, I’m unable to log in from this page or any child page of it (ie character or guild Armory pages): https://worldofwarcraft.blizzard.com/en-gb/
I select the Account button for the drop down, select “Log in” and it takes me to a white empty page, with just the word “unauthorized” on it. I get the same page if I try to use the “WoW Characters” button, yet pressing the Account Settings button takes me to my account settings.
The GM on the ticket suggested clearing cache and trying a different browser, both of which I had already tried prior to creating a ticket.
It occurred after there was an issue on the EU forums with people being unable to login, and a corresponding problem with the Armories pages not loading for people. Whatever fix was put in place caused my Armories to glitch so, as it had worked in the past, I logged out with the intention of logging back in again … but I’ve not been able to since.