BAPI_GOODSMVT_CREATE in parallel mode causes "plant data of the material XXX is locked" error - abap

Question

Currently, We're developing mass GI posting by parallelism, to reduce work time dramatically, because we have to post GI item about 300k+ at one day.
Problem
I know there is a restraint about BAPI_GOODSMVT_CREATE - You can't post same material simutaneously because of table lock, so I grouped materials like this :
It seems reasonable, so I make parallel job for each material number, which total 7 in example.
When I try process this process, SAP refused to process with error :
M3 897 : The plant data of the material XXX is locked by the user XXX
Question
The error is about plant data, not stock data - so it's really confusing about why this error happening.
Is there a more restraint about BAPI_GOODSMVT_CREATE?
Note 369518 won't help about this situation.
Any help would be appreciated!
Program Code
LOOP AT gt_matnr_collect INTO wa_matnr_collect.
WAIT UNTIL g_progs <= pa_wpnum.
g_progs = g_progs + 1.
CALL FUNCTION 'Z_PP_STAMP_PARA_DISTRIBUTE'
STARTING NEW TASK g_task DESTINATION IN GROUP DEFAULT
PERFORMING return_stamp_para ON END OF TASK
EXPORTING
p_matnr = wa_matnr_collect-gi_code
p_spmon = p_spmon
TABLES
p_list = gt_main_para_list
p_item = gt_main.
g_task = g_task + 1.
g_sprog = g_sprog + 1.
ENDLOOP.
gt_matnr_collect looks like this :
gt_main_para_list looks like this :
gt_main looks like this :
FM 'Z_PP_STAMP_PARA_DISTRIBUTE'
FUNCTION z_pp_stamp_para_distribute.
*"----------------------------------------------------------------------
*"*"Local interface:
*" IMPORTING
*" VALUE(P_MATNR) TYPE MATNR_D
*" VALUE(P_SPMON) TYPE SPMON
*" EXPORTING
*" VALUE(E_MATNR) TYPE MATNR_D
*" TABLES
*" P_LIST STRUCTURE ZSPP6030_PA_LIST
*" P_ITEM STRUCTURE ZSPP6030_PA_ITEM
*" R_RESULT STRUCTURE BAPIRET2 OPTIONAL
*"----------------------------------------------------------------------
DATA : gs_head LIKE bapi2017_gm_head_01,
gs_gmcd LIKE bapi2017_gm_code,
gs_doc LIKE bapi2017_gm_head_ret,
gt_item LIKE TABLE OF bapi2017_gm_item_create
WITH HEADER LINE,
gt_return LIKE TABLE OF bapiret2 WITH HEADER LINE,
gs_return LIKE bapiret2,
group_id(22) TYPE c,
l_begda LIKE p0001-begda,
g_last_date TYPE d,
lv_matnr TYPE ztpp5360-gi_code,
lv_batch TYPE ztpp5360-gi_batch,
lv_aufnr TYPE ztpp5360-arbpl,
lv_cnt(3) TYPE c.
CONCATENATE p_spmon '01' INTO l_begda.
e_matnr = p_matnr.
CALL FUNCTION 'RP_LAST_DAY_OF_MONTHS'
EXPORTING
day_in = l_begda
IMPORTING
last_day_of_month = g_last_date
EXCEPTIONS
day_in_no_date = 1
OTHERS = 2.
CONCATENATE p_matnr '*' INTO group_id.
LOOP AT p_list WHERE group_id CP group_id.
CLEAR : lv_matnr, lv_batch, lv_aufnr, lv_cnt.
SPLIT p_list-group_id AT '-' INTO lv_matnr lv_batch lv_aufnr lv_cnt.
CASE lv_batch.
WHEN 'EMPTY'.
lv_batch = ''.
ENDCASE.
p_list-status = 'WIP'.
MODIFY p_list.
LOOP AT p_item WHERE group_id = p_list-group_id.
MOVE : p_item-gi_m_q TO gt_item-entry_qnt,
* 'KG' TO gt_item-entry_uom,
'X' TO gt_item-withdrawn,
'3100' TO gt_item-stge_loc.
MOVE : '261' TO gt_item-move_type,
p_item-gi_code TO gt_item-material,
p_item-werks TO gt_item-plant,
p_item-aufnr TO gt_item-orderid,
lv_batch TO gt_item-batch.
APPEND : gt_item. CLEAR : gt_item.
ENDLOOP.
MOVE : g_last_date TO gs_head-doc_date,
g_last_date TO gs_head-pstng_date,
'03' TO gs_gmcd-gm_code.
REFRESH : gt_return.
CLEAR : gt_return, gs_doc.
CALL FUNCTION 'BAPI_GOODSMVT_CREATE'
EXPORTING
goodsmvt_header = gs_head
goodsmvt_code = gs_gmcd
IMPORTING
goodsmvt_headret = gs_doc
TABLES
goodsmvt_item = gt_item
return = gt_return.
READ TABLE gt_return WITH KEY type = 'E'.
IF sy-subrc = 0 OR gs_doc IS INITIAL.
CALL FUNCTION 'BAPI_TRANSACTION_ROLLBACK'.
LOOP AT p_item WHERE group_id = p_list-group_id.
p_item-ecode = 'E'.
p_item-msgtx = gt_return-message.
p_item-aedat = sy-datum.
p_item-aezet = sy-uzeit.
p_item-aenam = sy-uname.
MODIFY p_item.
ENDLOOP.
p_list-status = 'ERR'.
p_list-msgty = 'E'.
CONCATENATE gt_return-message '/' gt_return-id '/' gt_return-number INTO p_list-msgtx.
MODIFY p_list.
ELSE.
CLEAR : gs_return.
CALL FUNCTION 'BAPI_TRANSACTION_COMMIT'
EXPORTING
wait = 'X'
IMPORTING
return = gs_return.
IF gs_return-type = 'E'.
p_list-status = 'ERR'.
p_list-msgty = 'E'.
p_list-msgtx = gs_return-message.
ELSE.
LOOP AT p_item WHERE group_id = p_list-group_id.
p_item-gi_m_mblnr = gs_doc-mat_doc.
p_item-gi_m_mjahr = gs_doc-doc_year.
p_item-ecode = 'S'.
p_item-msgtx = ''.
p_item-aedat = sy-datum.
p_item-aezet = sy-uzeit.
p_item-aenam = sy-uname.
MODIFY p_item.
ENDLOOP.
p_list-status = 'FIN'.
p_list-msgty = 'S'.
p_list-msgtx = ''.
MODIFY p_list.
ENDIF.
ENDIF.
REFRESH : gt_item.
CLEAR : gs_head, gs_gmcd.
WAIT UP TO 2 SECONDS.
ENDLOOP.
ENDFUNCTION.