Re: Two outbound delivery as a Delivery note

This looks very weird.

the document flow for the second item does not yet have any billing document while the document flow for the first item has 2 billing documents.

I can also see that your material document has a custom tab.

This usually drives my mind into the assumption that it may be caused by wrong coding in user exits. You may need to compare other business cases where a second item was added to a sales order at a later time and where 2 delivery documents got created based on the delivery split criteria, to know if this is single case or if that happens all the time.

You should also look into the change history of your 2 deliveries and your sales order to know what was done (from my experience the change history is usually pretty long in such cases).

Try to redo the steps in the same timely sequence in your test environment.