question on ash

Hi Experts,

Could you please let us know why the sql_id in first query and event in second query is missing? What might be the reasons?

SQL_ID missing:
===============


SELECT count(*) , ash.SQL_ID
 FROM v$active_session_history ash , dba_users u
SQL>   2    3      WHERE u.user_id=ash.user_id and  ash.sample_time BETWEEN
     to_date('11-JUL-2023 13:00:00','DD-MON-YYYY HH24:MI:SS') and
     to_date('11-JUL-2023 15:00:10','DD-MON-YYYY HH24:MI:SS') and session_id=1251 and session_Serial#=44774 group by ash.SQL_ID order by 1;
  4    5
  COUNT(*) SQL_ID
---------- -------------
         3 6ahf5vfspanr9
        22 6s7t3fr05g14f
       997------------------------->Missing
      1483 27kxk9bpbnsqg
      1532 9thk3zwuxk927
      2597 67264jh510f32


6 rows selected.




Event name missing:
==================


SQL> select event,count(*),sum(time_waited)
from v$active_Session_history where session_id=1251 and session_Serial#=44774 group by event order by 2 desc  2  ;


EVENT