This issue has been identified as a product defect with ID 326648, to improve the way Change Auditor enumerate and resolve the network connection between the coordinator in the root domain and the foreign forest servers topology. This was fixed in Change Auditor 7.3 release.
WORKAROUND:
Option 1:
Fix the broken foreign forest sites by either adding the missing servers node back into their respective site OR deleting the empty site.
Option 2:
Install a local coordinator in the target foreign forest instead of deploying a foreign forest agent.
