Update query performance with some buggy behavior

Another odd behaviour related to this:- There is no such column as 'RID' in table MRQ, but this UPDATE runs without error in production. When we try to execute the SELECT part of the query(i.e. SELECT RID...) It's failing with "ORA-00904: "RID": invalid identifier" . So I wanted to understand , how did that Update happen/succeed then? I have captured the sql monitor for the same as below from prod. In any case, I was expecting the plan_line_id -7 ( SORT ORDER BY STOPKEY ) should have returned only ~20 actual rows(as we have rownum<=20 filter) and thus the table MRQ would have been full scanned Max ~20 times , but it's resulting ~13k rows and that many time the MRQ is getting full scanned. Are we hitting any bugs here because of the buggy way it's written by the team?

Also the execution time for this Update query is increasing day by day, must be because either the table GTT_TAB is having rows increasing day by day and thus the number of full tables scan increases for MRQ making the query response time increase. or the number of rows in table MRQ is increasing thus making that step-11 more CPU intensive for each full scan.

Below is the table and column stats.

Table MRQ having total ~2.3million rows.

COLUMN_NAME             NUM_DISTINCT                         DENSITY
                           NUM_NULLS             HISTOGRAM
RP_STX                             6
           2.11625295890333E-7                0
    FREQUENCY
R_DATE                             395
        0.0048780487804878                  0
  HEIGHT BALANCED
MRF_NM                             4
          2.11625295890333E-7                 0
    FREQUENCY
FR_NM                               30
          2.11625295890333E-7                 0

UPDATE GTT_TAB
   SET PRT = 999
 WHERE RID IN

          (SELECT RID
             FROM (  SELECT *
                       FROM MRQ
                      WHERE     R_DATE = TRUNC ( :B1) - 2
                            AND RP_STX = 'XX'
                            AND MRF_NM = 'YYY'
                            AND FR_NM NOT IN
                                   (SELECT L_VL
                                      FROM TLSV
                                     WHERE L_NM = 'XXXXXXX')
                   ORDER BY JE_ETS - JE_STS DESC)
            WHERE ROWNUM <= 20)

Global Information

 Status                                 :  DONE
 Instance ID                            :  4
 SQL Execution ID                       :  67108864
 Execution Started                      :  11/18/2021 18:15:25
 First Refresh Time                     :  11/18/2021 18:15:32
 Last Refresh Time                      :  11/18/2021 23:25:30
 Duration                               :  18605s

Binds

| Name | Position | Type |                                            Value
                                           |


========================================================================================================================


| :B1  |        1 | DATE | 11/19/2021 00:00:00
                                            |


========================================================================================================================

Global Stats