Hi- Amazon Developer Portal usually won't ask for login again if you click on "add upcoming version" link. I believe, there might be session time out when you tried and portal has been redirected to login page. Please try once again to upgrade your app. If the link is still redirecting to login page even for a valid session then please raise a ContactUs (
https://developer.amazon.com/help/contactus.html) with us for further information. Thanks!