Unable to get SID even concurrent program running normally

Dear All,

To understand what a concurrent program is doing in back end we use below query. it should give sid, But sometimes it is returning NULL value even the concurrent program running normally.

SELECT sid FROM v$session WHERE paddr LIKE

(SELECT addr FROM v$process

WHERE spid = (SELECT oracle_process_id FROM fnd_concurrent_requests

WHERE request_id = TO_NUMBER(&request_id)));

After some time we have observed that the Concurrent program has completed successfully.

The concurrent program is a  pl/sql program. It is happening not only for one program but also for various programs off and on.