Symfony 3.0.1 CSRF token present but invalid

In my case it was that the var/sessions/ folder wasn't writable. The default is var/sessions which is set at config.yml.

session:
    # http://symfony.com/doc/current/reference/configuration/framework.html#handler-id
    handler_id:  session.handler.native_file
    save_path:   "%kernel.root_dir%/../var/sessions/%kernel.environment%"

Make sure you have var/ folders writable.

chmod 775 -R var/sessions/
chmod 775 -R var/log/
chmod 775 -R var/cache/

I just had a similar issue with Symfony 3.2

The CSRF token is invalid. Please try to resubmit the form.

After hours, we finally found the issue was related to session.cookie_secure (https):

Our production environment uses https, thus forces cookies to be secured over https. The dev environment used http. After moving the dev from HTTP to HTTPS, problem was fixed.