We are on Magento1.7 using Varnish+nginx+HHVM. Frontend part of the website is fast but on the admin side specifically when there AJAX calls it will take a lot of time. I observed that disabling Varnish is making admin load quickly but unable to figure out why varnish is causing this problem. Please note that we have an instruction that not to cache admin part and yes we don't have cache issues but performance is killing us. Please help me with a way to solve this problem.