Recently in one of the CRM 2013 On-premises UAT environment, observed that all of a sudden Entity Audit Stopped for OOB Case entity and was not able to see New Value data in Audit History as well, instead saw a symbol.

Below is the screenshot for reference.

After a long time investigation, found that this was the problem with Audit records, created on Audit Change at Entity Level and Disabled Events on Case entity.

Ran the below query against the required database.

SELECT 
 AuditId,
 ObjectId,
 [Action],
 AttributeMask,
 ChangeData,
 ObjectTypeCode 
 FROM AuditBase
 WHERE 
 [Action] = 102 -- Audit Change at Entity Level
 AND ChangeData = 'TRUE' -- For Disabled Events
 AND ObjectTypeCode = 112 -- Case Entity Object Type Code
 ORDER BY CreatedOn DESC

Got some records in AuditBase table.

Ran the below query and deleted the records from Auditbase table and it resolved the problem.

Note: Take the back up of the CRM Database before performing delete operation.

Delete from 
 AuditBase 
 WHERE Action = 102 AND 
 ChangeData = 'True' AND 
 ObjectTypeCode = 112 

Refreshed the required case record and was able to see the New Value data in the Audit History.