ssh -A stopped working in macOS Sierra and keychain is not unlocked at login
It seems that the ssh keys are not loaded by default into ssh-agent.

This solved the issue for me:

Edit your ssh config

vi ~/.ssh/config


Add the following

Host *
    IdentityFile ~/.ssh/id_rsa
    AddKeysToAgent yes
    ForwardAgent yes


Find out more information on reddit discussion:
https://www.reddit.com/r/osx/comments/52zn5r/difficulties_with_sshagent_in_macos_sierra/