After the first coordinator server is successfully upgraded to version 6.5, the data-migration to the new ChangeAuditor database may still be running and preventing the second coordinator from connecting to the database as part of its upgrade.
The error message in the second coordinator log is:
Could not acquire Dblock on database
This issue is resolved in Change Auditor 6.5.192+
NOTE: This can also occur in later versions if you attempt to upgrade the first Coordinator and then proceed with upgrading the other Coordinators if the upgrade on the first one has not yet been completed. Wait for the first upgrade to complete first before moving on to the other Coordinators.