Environment: Debian Jessie, I-MSCP 1.3.15, PHP-FPM, PHP 5.6.29 (Debian), opcache.enabled = 1, apc.enabled = 1
Since upgrading to 1.3.15, the login to any Software written in PHP is not possible any more.
Entering correct credentials e.g. to to joomla! or owncoud redirect back to the login site without error message. Nothing to see in the Log files.
Server sessions or OPcache might create the problem.
Update: OwnCloud shows:
Update II: Not sure, if it is related with the update, but it coincidentally occurred after it.