Macs revert to old primary update server

Hi,

I recently migrated several organizations to a consolidated SEC.  Mac endpoint redirections were done per Der Flounder's advice on creating a package that uninstalls/reinstalls SophosAV, plugging in new update server information:

https://derflounder.wordpress.com/2014/09/02/deploying-sophos-enterprise-anti-virus-for-mac-os-x-9-x/

This works perfectly, except for two organizations, in which 50 or so endpoints mysteriously point themselves to the old primary update server.  In one case the old SUM/Sophos Managemenent Server is powered off.  Endpoints tend to revert after one or two days, showing "differs from policy."  I can force policy compliance in the SEC, and they will go back to the new SUM.  After a day or two they revert back to the old SUM.

Your assistance is appreciated!

Thanks,

Brandt