WPEngine Cache Exclusion
If you host your site on WP Engine, you may encounter some issues without cache exclusions being added. This is due to aggressive page caching (which is a good thing!), but it can be easily resolved by requesting that WP Engine setup a special cache exception.
To do this, simply submit a support ticket to WP Engine via their support portal and ask them to exclude a few url query variables from cache.
To make things really easy for you, feel free to copy and paste this sample ticket:
My site runs the ProjectHuddle feedback plugin and we need to bypass varnish caching for their cookie. The ProjectHuddle team has instructed us to ask you to place a cache exception for their cookie.
Could you please bypass varnish caching for the _wp_session cookie?