Database hang with sql from SYS user

Hi all,

in this morning, my database hang which many sessions ( nearly 60 sessions on both nodes) running the SQL on bellows from SYS user.

SELECT event,

       sql_id,

       sql_plan_hash_value,

       sql_opcode,

       session_id,

       session_serial#,

       module,

       action,

       client_id,

       DECODE (wait_time, 0, 'W', 'C'),

       1,

       time_waited,

       service_hash,

       user_id,

       program,

       sample_time,

       p1,

       p2,

       p3,

       current_file#,

       current_obj#,

       current_block#,

       qc_session_id,

       qc_instance_id,

       INST_ID,

       REMOTE_INSTANCE#

  FROM gv$active_session_history

WHERE sample_time >= :1 AND sample_time <= :2

After killing all the sessions to free locks in database, it works normally. Although I found all logs in it, I cannot see any procedure running during that time.