AutoNumber Primary Key In Database Starts Jumping Suddenly By Thousand Places

The above image is of a table which I need to update according to a new data on daily basis. As you can see when I added two records at the last , the AutoNumber primary key of the table jumped by thousands . I have used the following query to update the table

Code:
db.Execute "INSERT INTO D_Counterparty (CPTY_ENTITY_ID,CPTY_DESC)"_ & "SELECT Ctpy_Entity_Id,Ctpy_Entity_Legal_Nm"_ & "FROM NewCU LEFT JOIN D_Counterparty ON D_Counterparty.CPTY_ENTITY_ID=NewCU.Ctpy_Entity_Id"

I never changed the AutoNumber from incremental to random and I have also tried re-seeding it but had no success. Also when I inserted the sample values using a sample table ,the AutoNumber was working fine . Here's that query

Code:
db.Execute "INSERT INTO D_Counterparty (CPTY_ENTITY_ID,CPTY_DESC,) SELECT a,b, FROM sample"

I did not use join in this query ...