Delivery &1 contains items from delivery &2 (see long text)

What causes this issue?

Inconsistencies were discovered in the documents as goods movement was
posted. Items from another delivery were found in the delivery
document.

System Response

The system terminates processing in order to avoid inconsistencies in
the database.

How to fix this error?

Make a note of the activities that led to this error message and inform
your system administrator of them.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.