FosHttpCache uses a default, hardcoded user hash for anonymous users to save on performances.
PR FosHttpCacheBundle#274 added a consistency check on the hash that re-generates the hash using the session in order to prevent inconsistencies with expired / cleared up sessions.
The hash that gets generated for Platform's anonymous user does not match the hardcoded one. Since it depends on how the anonymous role is configured, it may change on any instance.
This causes anonymous requests to invalidate cached versions of pages, since the consistency check disables caches / varying.