Resolution:
If you have made lot of changes to data and you see performance issues, first run following and see if this fixes it.
Login to SQLPLUS to run this:

/*

* Gathering the statistics after the data migration.

* Please wait while the Script Gathers statistics for the schema.

*/

declare

      v_username varchar2(30) := '';

begin

      select user into v_username from dual;

      --dbms_stats.delete_schema_stats(  v_username ) ;

      dbms_stats.gather_schema_stats(  v_username, cascade=&gtTRUE ) ;

end;

/

If you still see issues please contact Support.

Thanks.