Standard event getting triggered but not calling custom package subscription.

hi,

We are calling our standard business event 'oracle.apps.ont.oip.statuschange.update' every time a sales order is booked . There are some orders for which an event is created  successfully by custom package and for some they are just triggered by standard event but are not getting Processed.

select count(1) from applsys.aq$wf_deferred

a where a.user_data.event_name = 'oracle.apps.ont.oip.statuschange.update' and a.user_data.event_key = '&eventKey'

and a.msg_state = 'READY';

These are events which are in READY status but are not being processed further nor they are entering into Error Queue.