RE: RetrieveRecordChange History Issue(The property provided was of type Microsoft.Xrm.Sdk.EntityReference, when the expected was of type Microsoft.Xrm.Sdk.Entity)
Hi Susritha,
It seems that you had performed association or disassociation operation between the target knowledgearticle entity and another entity.(1:N or N:N)
e.g:
I have a contact, and I removed him from a specific marketing list, then system will create a new event record called "Remove Members" in related audit history records.

Before the record is created, the web api was able to execute successfully, however, after creation of record, I encountered same error as yours.
Please remove any association or disassociation audit records of the target record, or take a record which only has CRUD operations to test the api again.
Regards,
Clofly