Did something happen with the site with regard to the cookie that remembers you are logged in?
I normally always stay logged in, but today when I came to site I was not logged in. So I logged in, clicked the check box to remember me and then closed my browser. Upon going back to the site, again I was not logged in.
Identical Behavior on four different browsers, three different devices, cache and cookies cleared, yada yada, etc etc.
Something has changed.