EDI: IDoc number is not unique, IDoc not reloaded

What causes this issue?

IDoc &v1& should be retrieved. However, this is not possible because
the document number was not unique in the tables transferred.

System Response

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

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.