Yes - it could be the reason. Or your tmp directory is in fact somewhere else. So I suggest to use other session storage service or adjust current.
Go to <epesi_dir>/data/ and edit config.php
You should see something like that at the end:
define('FILE_SESSION_DIR','/tmp');
define('FILE_SESSION_TOKEN','epesi_<long string>_');
You can switch to use database or
memcache to store session data. Memcache must be supported by your hosting. Database will work always.
To use database add in
data/config.php:
define('SESSION_TYPE','sql');
That's all.
Or you can change FILE_SESSION_DIR to use your data folder of epesi. For instance use data/sessions for that - create sessions folder and forbid access to read files from that with .htaccess (deny from all).
define('FILE_SESSION_DIR','<full epesi dir>/data/sessions'); // e.g /var/www/epesi/data/sessions
Then observe this folder for the files.
Regards,
Adam
PS. Sorry for the lag in the response - I've got some vacations.