Users (affects both Frontend and CMS - on same machine) are served a "white page". Completely blank, no error code (404, twig500 or whatever).

Apache error.log shows fatal error:
[Wed Nov 26 22:39:59 2014] [error] [client 87.193.191.41] PHP Fatal error: Invalid serialization data for DateTime object in /data/www/www.bvb.de/current/vendor/symfony/symfony/src/Symfony/Component/Security/Core/Authentication/Token/AbstractToken.php on line 157, referer: http://www.bvb.de/ger/Mannschaften/Tradition
[Wed Nov 26 22:39:59 2014] [error] [client 87.193.191.41] PHP Fatal error: Invalid serialization data for DateTime object in /data/www/www.bvb.de/current/vendor/symfony/symfony/src/Symfony/Component/Security/Core/Authentication/Token/AbstractToken.php on line 157, referer: http://www.bvb.de/

line 157 is the list(... of

public function unserialize($serialized)

{ list($this->user, $this->authenticated, $this->roles, $this->attributes) = unserialize($serialized); }

Attached are two session files of anonymous. One of them (broken) contains '0' in publishedDate, modificationDate etc.

The problem occurs periodically rather than related to specific load scenarios (computational load or concurrency load)

Switching to 5.3 is no option in a short timeframe.
The issue affects editor-users of the CMS critically on match days (~5/10 this season).