ORA-01591: lock held by in-doubt distributed transaction string

The first thing to do is to check the result of these queries:
Check the following table:

select * from dba_2pc_pending;
select * from dba_2pc_neighbors;
select * from pending_trans$;
select * from pending_sessions$;
select * from pending_sub_sessions$;

From the above queries keep all the value of LOCAL_TRAN_ID in each table and try to force commit or rollback.

ALTER SYSTEM DISABLE DISTRIBUTED RECOVERY;
EXEC DBMS_TRANSACTION.rollback_force('LOCAL_TRAN_ID')   
--this changed state prepared to forced_rollback after that
COMMIT ;
ALTER SYSTEM ENABLE DISTRIBUTED RECOVERY;
EXEC DBMS_TRANSACTION.PURGE_LOST_DB_ENTRY('LOCAL_TRAN_ID');
COMMIT;

Repeat each steps for each LOCAL_TRAN_ID, turn on recovery for distributed transaction
crosscheck these tables (must be empty):

select * from dba_2pc_pending;
select * from dba_2pc_neighbors;
select * from pending_trans$;
select * from pending_sessions$;
select * from pending_sub_sessions$;