Many of our existing Sites go dead when changing CNAME change from <Site Custom Name>.force.com to <domain>.live.siteforce.com . Any ideas on what to do?

We are in the process of transitioning serveral ORGs' sites to HTTPS their domain were added between 2010 and early 2013. Those domains are serving sites using http and CNAMEs are set as <Site Custom Name>.force.com and they have been working fine all these years.
Now in order to enable HTTPS on thos sites the CNAME must be changed to <domain>.live.siteforce.com but we noticed that for some ORGs this works and for some other don't. (Notice that ORG Id is not used because domains created before Summer '13 release must be set without the ORG Id (http://releasenotes.docs.salesforce.com/en-us/summer14/release-notes/communities_custom_domain_URL.htm)).

For the time being the best way to determine if the CNAME change from <Site Custom Name>.force.com to <domain>.live.siteforce.com will work is to execute nslookup <domain>.live.siteforce.com if the name is resolved we can do the switch but if it doesn't resolve the site goes dead.

Cases Opened where salesforce have not been able to pinpoint the problem:

• #13022163 Org ID:00DG0000000h1Ws CNAME to sites not working site is DOWN 
• #13007608 Org ID:00DA0000000BrK9 Enable HTTPS in Sites and set CNAME target
• #13005559 Org ID:00DE0000000Y9b3 CNAM for Sites NOT Working
• #13009084 Org ID:00D300000000MyI Enable HTTPS in Sites and set CNAME target

References: 

• http://releasenotes.docs.salesforce.com/en-us/winter15/release-notes/rn_networks_https_domains.htm
• http://releasenotes.docs.salesforce.com/en-us/summer14/release-notes/communities_custom_domain_URL.htm
• https://help.salesforce.com/apex/HTViewSolution?urlname=Custom-Domain-and-CNAME&language=en_US
• https://help.salesforce.com/apex/HTViewSolution?urlname=Setting-Up-Custom-Domains-for-Salesforce-Sites-and-Setting-up-HTTPS-Support-for-Branded-Custom-Domains

Many of our existing Sites go dead when changing CNAME change from <Site Custom Name>.force.com to <domain>.live.siteforce.com . Any ideas on what to do?

We are in the process of transitioning serveral ORGs' sites to HTTPS their domain were added between 2010 and early 2013. Those domains are serving sites using http and CNAMEs are set as <Site Custom Name>.force.com and they have been working fine all these years.
Now in order to enable HTTPS on thos sites the CNAME must be changed to <domain>.live.siteforce.com but we noticed that for some ORGs this works and for some other don't. (Notice that ORG Id is not used because domains created before Summer '13 release must be set without the ORG Id (http://releasenotes.docs.salesforce.com/en-us/summer14/release-notes/communities_custom_domain_URL.htm)).

For the time being the best way to determine if the CNAME change from <Site Custom Name>.force.com to <domain>.live.siteforce.com will work is to execute nslookup <domain>.live.siteforce.com if the name is resolved we can do the switch but if it doesn't resolve the site goes dead.

Cases Opened where salesforce have not been able to pinpoint the problem:

• #13022163 Org ID:00DG0000000h1Ws CNAME to sites not working site is DOWN 
• #13007608 Org ID:00DA0000000BrK9 Enable HTTPS in Sites and set CNAME target
• #13005559 Org ID:00DE0000000Y9b3 CNAM for Sites NOT Working
• #13009084 Org ID:00D300000000MyI Enable HTTPS in Sites and set CNAME target

References: 

• http://releasenotes.docs.salesforce.com/en-us/winter15/release-notes/rn_networks_https_domains.htm
• http://releasenotes.docs.salesforce.com/en-us/summer14/release-notes/communities_custom_domain_URL.htm
• https://help.salesforce.com/apex/HTViewSolution?urlname=Custom-Domain-and-CNAME&language=en_US
• https://help.salesforce.com/apex/HTViewSolution?urlname=Setting-Up-Custom-Domains-for-Salesforce-Sites-and-Setting-up-HTTPS-Support-for-Branded-Custom-Domains