Outline was ignored by sql, after migrated into sql plan, it worked, but this morning, it didn't wor

We had outline on this sql to force to use the index PRT_PRCS_IDX1 instead of IDX9M, it was perfectly working for a long time.

SELECT pp.prt_process_no
from prt_process pp,prw_contr_state pcs,prw_valid_trans pvt
where pp.prt_process_no > :p1 AND prt_sys_status (pp.prt_status_code) NOT IN (:"SYS_B_0",:"SYS_B_1") AND pvt.prw_transition_id = :p2 AND pcs.prw_control_id = pvt.prw_control_id AND pp.prt_type_code = pcs.prt_type_code AND pp.prt_class_code = pcs.prt_class_code AND (pp.prt_subclass_code = pcs.prt_subclass_code) AND (pp.prt_status_code = pcs.prt_status_code OR pcs.prt_status_code IS NULL) AND (pp.prt_priority_code = pcs.prt_priority_code OR pcs.prt_priority_code IS NULL) AND (pp.resp_code = pcs.prt_resp_code OR pcs.prt_resp_code IS NULL) ORDER BY prt_process_no