We have one document library that started showing the error ' An item with the same key has already been added. ' for all files when trying to edit the metadata of the file.

I can't seem to find any occurences of the problem on the web. Has anyone here ever encountered the problem? If so, how do I fix it?

Additional information:

  • SharePoint Online
  • The Document Library has Document Sets
  • Problem occurs for both properties of the document sets and files inside document sets
  • When using 'Quick edit' the properties can be edited
  • No duplicate files
  • No document approval flow
  • Besides the document set, it's a vanilla document library


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