In Magento 2 on cart page checkout button asking for login again no matter I am already login why ? How to skip this login if i am already login ?
This problem is available due to you have keep cache disable in your site.
If you enable cache in your system, You dont ask for login again in popup box in cart page.
This is default bug in magento 2 when cache is disable at that time you have to ask for login again in cart page.
Still magento 2.1 version this bug is not solved by magento team.
This is listed in github issue list.
You can go directly checkout page using click on go to checkout button inside minicart at top or directly set checkout url in your browser.