Indeed I found these errors in the logs when deploying the new package:
2009-07-30 17:52:56 MEST [ISS.0099.0003E] Unable to create Broker Transport BRK_FLO_11320__alfas_pfi_b2b.trigger_sendData_trigger. Exception com.wm.app.b2b.server.dispatcher.exceptions.TransportException: [ISS.0098.9014] BrokerException: Out of Range (221-3429): The shared document ordering value in the client's descriptor is not a valid value for this Broker.
2009-07-30 17:52:56 MEST [ISS.0098.0036C] alfas_pfi_b2b.trigger:sendData_trigger encountered Transport Exception: [ISS.0098.9014] BrokerException: Out of Range (221-3429): The shared document ordering value in the client's descriptor is not a valid value for this Broker.
I don’t know what a “document ordering value” is… 
No change was supposed to be made by the delivered either on the document or the trigger: all concerned parameters were the same.
The queue was empty before and during delivery.
Thanks for your support!
#webMethods#Integration-Server-and-ESB#broker#Universal-Messaging-Broker