Varnish not fully working

On my virtual server is Varnish installed. I am not allowed to change and upload the default vcl file myself. My provider does that for me, so I can not tweak and try and error myself. Since my server was upgraded with PHP7 and Varnish it is super fast. But we concluded that Varnish is not fully working. Also checked it on http://www.isvarnishworking.com/. It says Yes! Sort of!

According to my provider it’s probably because of a cookie
Cookie: SESSa3a0af0bcc6bd3d2e3fd2ed957501625=hFBaeTD4gRF6caRzfBolBzrto6j1oQs64Ic8d4O9ffw
I have smartIp and Google anayltics installed.

Thereby my drupal-site places Cache-Control: no-cache, must-revalidate.

Can someone help me with this?

Drupal version: 


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