Check Email breaks Pantheon Varnish Cache

Hi! I found out that this awesome plugin is breaking somehow pantheon varnish cache, I had to disable it to be able to run the site and get varnish up and running.

https://pantheon.io/docs/varnish/#debugging-cookies-and-varnish
I got to find out it was the plugin, so I want to know if you could give it a look later to check what cookie may be the responsible of this behavior.

Thanks!