Refreshing Materialized view in 11g hangs

Dw is the owner of the Materialized View.
Sowadw is the user that client uses to refresh this MV. She used to do this very fast in 9.2
Now in 11.2 is hanguing.
 
CREATE MATERIALIZED VIEW DW.DW_TBS_TASKS 
TABLESPACE DW_DATA
NOCACHE
LOGGING
NOPARALLEL
BUILD IMMEDIATE
REFRESH FORCE ON DEMAND
WITH PRIMARY KEY
ENABLE QUERY REWRITE
AS 
/* Formatted on 5/5/2014 8:07:41 AM (QP5 v5.185.11230.41888) */
SELECT DOCUMENT_NUMBER,
  TASK_NUMBER,
  TASK_STATUS,
  TASK_PRIORITY,
  SCHEDULED_COMPLETION_DATE,
  ACTUAL_COMPLETION_DATE,
  ESTIMATED_COMPLETION_DATE,
  LAST_MODIFIED_USERID,
  LAST_MODIFIED_DATE,
  TASK_TYPE,
  CIRCUIT_DESIGN_ID,
  WORK_QUEUE_ID,
  WORK_QUEUE_PRIORITY,
  ASSIGNED_FROM_WORK_QUEUE,