I am trying to figure out why my Magento 2.2.6 shop is showing the header:
vary: Accept-Encoding,User-Agent
The problem is that the "User-Agent" makes my cache not working in a good way.
My shop is built like:
Visitor -> Nginx SSL Termination -> Varnish -> Apache 2.4
(This is under DirectAdmin with http2 activated.)
How can I find out where the Vary: User-Agent is added?
I have been looking in the Nginx config, Varnish default.vcl, and .htaccess
No luck, can you guide me where I should begin, and what I should look for?
(The problem is the same in production mode)