When you rename the OU that contain computer account for exchange server, or if you move exchange server from one OU to another, Exchange will generate this warning:
Event ID: 9186
Microsoft Exchange System Attendant has detected that the local computer is not a member of group 'cn=Exchange Domain Servers,cn=Microsoft Exchange Security Groups,dc=domainname,dc=com'. System Attendant is going to add the local computer into the group.
The current members of the group are ********* and add some DNs for the group members
This warning sometime followed by an Error from MSExchangeSA as well indicating it tried to add the computer account to the group and it failed with event ID 9187.
This is due to the natural behavior for system attendant service as by design, when this service start at the first time it cache the Distinguished Name for the Exchange server computer account, and when this DN changes it require to be reflected on the MSExchangeSA service cache, to flush this cache only we need to restart MSExchangeSA service by services.msc console or by powershell and this events will go away.