Your browser isn't retaining the cookies which enable you to be identified.
So, which browser (Internet Explorer, Edge, Chrome, Firefox, Safari, Dolphin, etc) and which device (Windows PC, Mac, iPad, Android phone, etc) are you using, please?
I suggest trying some of possible solutions that people have put forward.
The ones which suggest accessing the 'Usernames & Passwords' section, completing deleting any reference to the relevant website(s), such as AB, and clearing the cache seem among the most likely to succeed to me.