Its been an issue since a while with WooCommerce not fully compatible to Varnish Caching on WordPress Forum . As we all know that Varnish is a caching system deployed on the front-end of the server that handles HTTP requests. It speeds up the web application’s performance by a significant margin (Varnish-cache.org official statement claims that it speeds up the performance by 300 to 1000 times.)
Cloudways team research on this issue and get a solution on their platform in which Varnish are now friendly with WooCommerce. They have some load testing performance screenshots here: Varnish Compatibility WooCommerce
Read the whole case study on how Cloudways made WooCommerce Varnish compatible.