After system update using
yum update command and server reboot, websites are not accessible with Apache default page shown. Apache restart helps to fix the issue, but after the server reboot the issue re-appears.
Watchdog starts up the monitored services before network service is enabled.
Bug #PPPM-3457. It is fixed in Plesk 12 MU #70, Plesk 12.5 MU #10 and Plesk Onyx.
Install the latest microupdates or upgrade to the latest Plesk version.