Crap! There is definitely a problem… The browser where I’ve logged in before works fine, but elsewhere there are JavaScript errors.
If anyone has time to try and see what might be causing the problem, please let me know. Worst case is I’ll do a reinstall on a fresh server tonight and migrate the data over.
*EDIT: In the meantime do not log out!
*EDIT 2: The issue does not appear to be related to my attempted breaking of the servers (the problem is replicated on the staging server which I mercifully left up after the upgrade). I have also tested it against multiple desktop browsers (Opera, Firefox, Safari, Chrome) and got the same result.
I have a sneaky suspicion it might be related to a plugin. Specifically, the one we use to display the ad. Will be able to test more later.
For now there appears to be a workaround — go to an article, click “Continue Discussion”. A version of the site will load with a login button at the top.