I am having exactly the same issue on version 1.7.6.4. Both the product listing page and module page worked once and now they always redirect to the login. When I look into my file manager, in the ect folder, I don't see anything related to nginx, and debug mode isn't showing anything. The page just redirects the the login and that's it. I've also tried eliminating the cookies and nothing changed.
Can someone please help me out??