When using Azure API to migration deleted users for Document Libraries to SPO certain properties are used for 'Created By' & 'Modified By'
This properties are:
'Document Created By'
'Document Modified by'
Out of the box the properties should match the 'Created By' & 'Modified By' but for unknown reason or SharePoint customization they can be different, incorrect or missing.
Use the attached SharePoint Item Transformer to map 'Created By' & 'Modified By' to 'Document Created By' & 'Document Modified by' respectively
The following link is to a KB article that describes how to generally use a Transformer:
