AIP Scanner file share "Last Modified By" empty

We run the scanner against to file share and SharePoint Server 2016. In the scanner report we see for SharePoint the correct "Last Modified By" user but for file share all "Last Modified By" user are empty. On a Office document on a file share there also the "Last Modified By" user in the metadata. Why ist this user not in the scan report?

thanks for you advise,
Martin