Facing issue to fetch proposed value of Pending Transactions

We are trying to fetch proposed valued of pending transactions. Transaction is on Assignment change, I have written the following code but getting ORA19011: "Character string buffer too small"

SELECT
person.person_number
,txnH.xml_data_cache
,EXTRACTVALUE(xmltype('<root>'||txnH.xml_data_cache||'</root>'),'root/TRANSACTION/TransCtx/ActionCode/newValue') reason

FROM hrc_txn_header txnH,
per_all_people_f person,
per_all_assignments_m asg,
per_person_names_f names,
hrc_txn_data txnD,
FA_FUSION_SOAINFRA.WFTASK wft,
per_persons ppos

WHERE UPPER (txnH.Object) IN ('PER_ALL_ASSIGNMENTS_M')
AND txnH.object_id = asg.assignment_id