I was having that problem too and I found one thing that helped was not opening product in new windows. I usually open several windows of product I want, log in once, then add them all, but that wasn't working for me here this week - each new window behaved as if I hadn't already logged in. I had to always work within the same window - log in, ad one product, click 'continue shopping, add the next, and so on. It took a bit more time but was worth it for the deals
Maybe that will help you?