Data validation is not happening even though we have a unique index for DMS replication instance version 3.5.4

Question

We are performing data migration from On-Prem DB2 LUW to AWS Aurora PostgreSQL using AWS SCT and DMS. While the data load is successful, data validation is not occurring despite having a unique index for DMS replication instance versions 3.5.3 and 3.5.4. However, data validation is successful with DMS replication instance version 3.5.2.

Table and Unique Index Details:

CREATE TABLE xyz (
  xxx CHARACTER VARYING(22) NOT NULL,
  xxx_dt DATE NOT NULL,
  xxx_cd SMALLINT NOT NULL,
  zxxx_cd CHARACTER(7),
  state_xxx CHARACTER(2),
  xxx_reading INTEGER,
  xxx_uom CHARACTER(1),
  xxx_nb CHARACTER VARYING(17),
  xxx_id INTEGER NOT NULL,
  xxx_in CHARACTER(1) NOT NULL,
  xxxn_in CHARACTER(1) NOT NULL);

CREATE UNIQUE INDEX ip_xxx
  ON xyz (xxx ASC, xxx_dt ASC, xxx_cd ASC, state_xxx ASC, xxx_reading ASC, xxx_nb ASC) NULLS NOT DISTINCT;