If you respond to a PM notice or other notification without being logged in then on the error page you get you also must be sure that you checked Remember Me.

If you use an setting in your browser or an app that remembers your login you still have to make sure that the box is checked. Log in from the site if you have problems and that will hopefully colve the problem. Deleting your old bookmark and resaving it after a new login also gets rid of any old and inaccurate login.

You must save cookies for this all to work period! All of these features are dependent on cookies, so you must enable them.

Cookies are not some insidious hacking attack, they have been used since the beginning to allow your browser's cache to recall sites and settings without having to log in over and over and try to remember everything you did there.

And one more thing. If you use a so-called 'privacy browsing' mode then your cookies aren't necessarily going to be saved, so Yes, this will happen to you.

(And you ain't private nohow, the ISP and site still see you, your settings just won't stick or be found in the browser's History)

And Come On! I doubt there is any reason to be a Secret Squirrel here...