Mload error - 2794 - UPI is an identity column

Greetings Experts,
Recently we are facing a recurring Informatica job failure with "External Loader Error" with UPI defined on the identity column with max value 2147483646 (Mload defined on the staging table with UPI on an identity column called "id").  We could see that the max value for the column loaded into this Mload staging table for this load (400000000) is well less than the max value.  From the UV table we could see that the dbcerror code is 2794, indicating duplicates on the PI.
Are the duplicates being generated from the identity column id?  If yes, why does identity column generate duplicates (we have around 35 records in UV table, all this 35 PI value also exists in the target staging table there by causing duplicates on PI column)
If not, what might be the issue leading to the failure.
Thanks for your time on this.