How long your session last? in OVH?
Remember that PHP configuration has it's own session management make sure you know it and match on your CI application need.
Here how I configure my php.ini
session.gc_maxlifetime = 900 (15 minutes)
For My CodeIgniter Configuration
$config['sess_expiration'] = 900; (15 Minutes)
$config['sess_time_to_update'] = 450; (7 half minutes for update)
There are those who tell lies with meaning behind them and those meaning less lies!