Rails 4 + Devise: sign_in(user) method not working, does not set current_user

I figured it out. In my @checkout form object, I update the guest_users attributes and save it when I call @checkout.save. I think devise has to sign in the most recent version of guest_user, so I had to add a guest_user.reload before sign_in(guest_user)

In short, reload your user (user.reload) before signing it in.