Plesk 12 server intermittently displays default plesk page

[EdmondC]

I know this issue has been touched by several people already, however, I have not found a solution to my problem. I am migrating my old environment from Plesk 10.4.4 on Ubuntu 10.04 to Plesk 12.0.18 on Ubuntu 14.04. I was able to migrate the sites from the old server over to the new server with little issue. The new server configuration with Apache and Nginx wasn't working for me, so I disabled Nginx and reconfigured all domains. I moved each site over one at a time and tested them, resolving issues when they arose, and moved on to the next domain. One thing I did not notice at the time, was the server would intermittently display the default parallels index.html page on the sites. I would test one site, see it is working, and move to the next, etc. I would then retest the sites and they would display the index.html page. I have tried reconfiguring each domain, restarting Apache to no avail. One site I have is a static site, whereas all of the others are Drupal sites. The static site would display once Apache was restarted, but will go back to the default page after a while. The same thing occurs with the Drupal sites as well. It is just like the sites are shutting down for some reason.
I have checked the log files, and have not come across anything out of the ordinary. I have followed several threads which discussed DNS. The issue occurs when DNS is turned on, and when it is turned off. I do not use DNS on the server since the DNS records are being managed elsewhere. I have even added the correct name servers under each subscription in our system. I have used the Web Server Configuration checker and receive one warning. I followed the steps in http://kb.parallels.com/en/112815. I queried the psa database retrieving an Empty set (0.00 sec). Nothing seems to work. One minute the site is there, the next is the default page. As of right now, I am unable to put this server into production since it is not behaving as it should. Does anyone have any idea what may be causing this to occur?

 

[EdmondC]

I have found my issue. Before I started the project, I decided to re-use IP addresses on the old server which were not currently assigned to a production site. I removed the IPs and assigned them to the new server. I was able to set up everything and move over the sites. Somehow those IPs were re-associated to the old server. I didn't realize this until this morning when I happened to look at the Apache error logs on the old server and saw entries for the domain I was testing. I then tailed the log file and accessed the site being tested. To my surprise, the log file showed entries for that site. I then logged into the old system's panel and looked at the IP addresses. They showed the old IPs until I clicked on the Reread IPs button. Once I did this, the new IPs showed up in the old system. I removed those IPs and clicked Reread IPs once again. They did not show back up. I then tested the site again and it came up on the new system. The sites have been consistently refreshing without issues.
I can now finish migrating everything over to the new system and shutdown the old server.