no_cache_reason: "Caching disabled for session (nocache cookie set)"

This might be a bug. The cookies nocache and nocache_temp are set whenever there is a message waiting in the session during hook_exit. During the next page request, authcache makes sure that the page is not served from the cache in order to have an opportunity to display the message to the user.

However I suspect that only nocache_temp should be set in hook_exit and that the nocache serves a different purpose. From what I understand the nocache cookie is supposed to exclude a whole user session from the cache - and not only one request.

Would you please try and comment out line 509 from authcache.module and report back whether it improves the situation. Alternatively you also may just apply the attached patch.

 495 /**
 496  * Implements hook_exit().
 497  *
 498  * Called on drupal_goto() redirect.
 499  * Make sure status messages show up, if applicable.
 500  */
 501 function authcache_exit($destination = NULL) {
 502   global $_authcache_is_cacheable;
 503 
 504   if ($destination !== NULL) {
 505     $_authcache_is_cacheable = FALSE;
 506 
 507     // Cookie will inform Authcache not to display cached page on next request
 508     if (drupal_set_message()) {
 509       setcookie('nocache', 1, 0, ini_get('session.cookie_path'), ini_get('session.cookie_domain'), ini_get('session.cookie_secure') == '1');
 510       setcookie('nocache_temp', 1, 0, ini_get('session.cookie_path'), ini_get('session.cookie_domain'), ini_get('session.cookie_secure') == '1');
 511     }
 512   }
 513 
 514   //TODO:probably move _authcache_shutdown_save_page() code to here if this works
 515   _authcache_shutdown_save_page();
 516 
 517 }

There are two other places the nocache cookie might get set.

1. When someone clicks on "Disable caching for this browser session" in the authcache debug widget the cookie is set.
2. Upon login when the has_js cookie is missing

You could try to force the cookie-value by placing the following line of code at the end of your settings.php file:

$_COOKIE['has_js'] = '1';