When using the Approved Email Query APPROVED_EMAIL_VAULT_QUERY, the OR operator is not bringing over required documents.
When applying the OR operator in a query, do not use () as a field separator.
Example: (myCustomField__c='OH') OR (myCustomField__c='CA')
To correct this issue, use the following syntax:
myCustomField__c='OH' OR myCustomField__c='CA'
CRM Help Documentation: Integrating CRM and Vault for Approved Email