I am trying to migrate a SharePoint 2013 to SharePoint Online. The 2013 site has numerous document libraries which went all fine to migrate using the SharePoint Migration Tool. Except one library. I end up getting Error 0x01310007 - "Failed to Read the file:Could not retrieve file's metadata". For each of the 500+ documents.
I have all the necessary user rights to access the files and the document library. I was able to successfully migrate the 30+ other document libraries with the same account. I tried different versions of SPMT. I tried most things with no luck.
Googling the error code doesn't make me wiser. It appears to be a pretty generic error message that could mean anything. I found a handful of forums where other people ran into the same issue but no real solution to it.
I do think I might have a clue what may be causing the problem in my case. I did not install or configure the original SharePoint 2013 server. But I discovered that the SharePoint is running a scheduled task. A homemade C# code that reads data from the company's 3rd party customer database and then updates metadata in the problem document library. For example, when a customer is marked "obsolete" in the 3rd party database - the corresponding documents in SP are also marked as obsolete. So the staff can easily tell in SharePoint which documents are current and which are obsolete.
The C# executable was coded some 7+ years ago by an IT company that no longer exist. I don't have any means of tracking down the actual person who once made the code. And I do not have the source code. Just the executable. There's no reasonable way to tell exactly what the code really do and how it access the document metadata. All I know is that if you do change a customer to "obsolete" in the 3rd party database, documents in SP for the same customer will also be updated with "obsolete" in a status field soon enough.
I suspect the code makes changes to the metadata in a way that SPMT fails to make sense of it when I try to migrate. I wouldn't know how or by what syntax. Maybe the C# code is adding a colon or comma too much in some metadata field. Maybe it's replacing SharePoints own metadata.
Is there a way to see the metadata associated with each file in a Document Library in the SQL Server content database? I am not really sure what I expect to find or even what I'm asking. I just imagine I could compare metadata for files in libraries I was able to migrate without problem with metadata for files in the problem library.
(I am absolutely not looking to migrate the mysterious C# executable to work with SharePoint Online. I just want to migrate the document library that seemingly have strange metadata)