OS version indicators in package release version strings (cos6, rhel6) of installed packages vs. update candidates (from autoinstaller3.log). Versions of the packages you have updates for at download site for RedHat el6 x64 (older; likely installed) and CentOS 6 x64 (newer).
Also I suggest checking your Yum repositories configuration for anomalies. Normally you shouldn't have repos pointing to autoinstall.plesk.com unless Autoinstaller is running.
Also I suggest checking your Yum repositories configuration for anomalies. Normally you shouldn't have repos pointing to autoinstall.plesk.com unless Autoinstaller is running.