Tersune... Sorry to say that is not deeper at all... Many have been seeing that for quite some time now...
The frustrating thing is the login errors keep changing for persons in different ways at different times.
I don't know if that is multiple loginservers that are not set up exactly the same and that they might react with different type of configurations/system settings/browser versions/coockies or whatever with different users...
For myself I've had all of the problems that have been discussed here, and since I made a really unscientific approach when I got it fixes as I was getting fed up/frustrated/angry (and more) and just did a lot of deleting of cookies/blocking services/scripts etc, I really don't have any idea what I did to actually make it work, or if I even might have become lucky and landed on a healthy login-server...
But at least it is stable for me now and have been for several days on both Chrome and Firefox.
That might change after tomorrows update though... lol
/Key