Hello. I'm using Magento 2.1.2 and I had a problem.
Sign in menu is missing. So, customer hard to sign in without buy produt. It just only create account menu.
Anyone can help me how to show "sign in" and "sign out" back
Looking at the problem you mention - it seems like its theme issue !
Can you please confirm that are you using any other premium theme or custom theme on the same ?
if yes then switch back to luma theme from the backend and then check it again !
Hope it helps !