SEARCH ALL not working in COBOL -Microfocus on UNIX Platform

Code looks like below.

       01  T1-DS-FDBK-TBL.
           05  T1-DS-FDBK-ENTRY  OCCURS  999 TIMES
                                     ASCENDING KEY IS T1-DS-FDBK-UNIT
                                     INDEXED BY T1-NDX.
               10  T1-DS-FDBK-UNIT         PIC X(4).
               10  T1-DS-FDBK-RPTIND       PIC X(1).

.

.

    SEARCH ALL T1-DS-FDBK-ENTRY
        AT END MOVE 'Y'                TO WS-FDBK-TO-RPT-SW
         WHEN T1-DS-FDBK-UNIT(T1-NDX) = WS-DIV-SUB
              MOVE T1-DS-FDBK-RPTIND(T1-NDX) TO WS-FDBK-TO-RPT-SW
    END-SEARCH.

I actually don't find any reason, why binary search would not be successful.