My experience -
My 'normal' mode is to play 3 worlds, each in it's own tab, using Chrome - all from a single account login.
A recent change (last week or two?), is if I change focus to a different tab (this game or any other web page) after a few minutes I need to reload and re-log back in to one of the 3 tabs if I go back to a tab that was previously open, active and working fine.
Today, I managed to log in to one tab and world OK - but trying to log in via the second tab got me a 'too many redirects' error screen, on the change server screen.
Trying to log into the 3rd screen gets me to a page that simply says 'Service' at the top of the screen, and beneath states 'method not allowed'.
My best guess is the desire to stop multi-accounts or subs has also prevented the previously legitimate system of a single account playing across multiple servers / worlds, each from a separate tab.
If so, it is very, very poor coding, and worse QA.
Playing via Firefox is a little better (not much), but that kind of misses the point of coding for the most popular browser in the world, doesn't it?