Internal Server Error 500 No response from subprocess (/usr/local/cpanel/whostmgr/docroot/cgi/addon_unixyvarnish.cgi) with exit signal: 1
The above error is fixed starting from the 1.6.2 release of the cPanel Varnish Plugin and the 1.2.2b release of the cPanel Varnish Nginx Plugin. If you don't know your plugin version it can be obtained from this file on your server: /etc/varnish/unixyvarnish.version
Be sure to forward the above instruction to your server support for assistance.