Oracle 10g To 11g Upgrade Performance

After upgrade 10g to 11g, the below sql is not working. I have issue with connect by, if we use it with subquery it will hang.

select item_code
from bom_list_pos
where ln_id in (select ln_id
from bom_list_nodes
start with ln_id IN (select ln_id from bom_used_work_pack where rownum =1)
connect by prior ln_id = parent_ln_id)

I ran 10g, able to get it less than minute, but 11g hang. below is explain plan.

11g explain plan
-----------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 19 | 209 | 148M (1)|494:23:18 |
|* 1 | FILTER | | | | | |
| 2 | TABLE ACCESS FULL | BOM_LIST_POS | 810K| 8711K| 7484 (1)| 00:01:30 |
|* 3 | FILTER | | | | | |
|* 4 | CONNECT BY NO FILTERING WITH SW (UNIQUE)| | | | | |
| 5 | TABLE ACCESS FULL | BOM_LIST_NODES | 46041 | 449K| 241 (1)| 00:00:03 |
|* 6 | FILTER | | | | | |
|* 7 | COUNT STOPKEY | | | | | |
| 8 | INDEX FAST FULL SCAN | UWPD_LN_FK_I | 1 | 5 | 2 (0)| 00:00:01 |

-----------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter( EXISTS (SELECT 0 FROM "M_SYS"."BOM_LIST_NODES" "SYS_ALIAS_1" WHERE "LN_ID"=:B1 START
WITH EXISTS (<not feasible>)
3 - filter("LN_ID"=:B1)
4 - access("PARENT_LN_ID"=PRIOR "LN_ID")
filter( EXISTS (<not feasible>)
6 - filter("LN_ID"=:B1)
7 - filter(ROWNUM=1)

-------------------
10g explain plan
--------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 440 | 9240 | 27 (4)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID | BOM_LIST_POS | 88 | 704 | 6 (0)| 00:00:01 |
| 2 | NESTED LOOPS | | 440 | 9240 | 27 (4)| 00:00:01 |
| 3 | VIEW | VW_NSO_2 | 5 | 65 | 2 (0)| 00:00:01 |
| 4 | HASH UNIQUE | | 5 | 30 | | |
|* 5 | CONNECT BY WITH FILTERING | | | | | |
| 6 | TABLE ACCESS BY INDEX ROWID | BOM_LIST_NODES | | | | |
| 7 | NESTED LOOPS | | 1 | 16 | 1 (0)| 00:00:01 |
| 8 | VIEW | VW_NSO_1 | 1 | 13 | 1 (0)| 00:00:01 |
|* 9 | COUNT STOPKEY | | | | | |
| 10 | INDEX FULL SCAN | UWPD_LN_FK_I | 122 | 366 | 1 (0)| 00:00:01 |
|* 11 | INDEX UNIQUE SCAN | LN_PK | 783 | 2349 | 0 (0)| 00:00:01 |
| 12 | NESTED LOOPS | | | | | |
| 13 | CONNECT BY PUMP | | | | | |
| 14 | TABLE ACCESS BY INDEX ROWID| BOM_LIST_NODES | 5 | 30 | 2 (0)| 00:00:01 |
|* 15 | INDEX RANGE SCAN | LN_LN_FK_I | 5 | | 1 (0)| 00:00:01 |
|* 16 | INDEX RANGE SCAN | LP_LN_FK_I | 88 | | 1 (0)| 00:00:01 |

--------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("PARENT_LN_ID"=PRIOR "LN_ID")
9 - filter(ROWNUM=1)
11 - access("LN_ID"="$nso_col_1")
15 - access("PARENT_LN_ID"=PRIOR "LN_ID")
16 - access("LN_ID"="$nso_col_1")