Nothing as far as I'm aware of. Is there anything in the error log files to provide a clue?
Since yours seems to be a 'random' problem, my thoughts are along the lines that it probably has something to do with the SESSION data/handling.
Probably a longshot, but with *one* of the many hosts I've worked on I came across a problem where the admin sessions were timing out prematurely, and I traced this back to the PHP
session.gc_maxlifetime being set to an abnormally low value as a result of a PHP upgrade.
http://stackoverflow.com/questions/3...ut-too-quickly
Although I state this was a problem with the admin functions, it is quite likely that a similar issue would have been occurring with the non admin functions as well and the admin simply noted the problem before any customers reported it as an issue.
As I say, it's a longshot....
Cheers
RodG