Automated upload competing with users who have a file open in Co-authoring mode

I haven’t experienced this specific issue, but I have seen related behavior in SharePoint Online. If a file is opened by someone, even if they are only viewing it, SharePoint may treat it as an edit session, which prevents metadata updates. In those cases, SharePoint shows the familiar message:

“The file is locked by \<user\>.”

This happens because users with Edit permissions often open documents in Edit mode by default, even when they only intend to read the content. That passive edit session can block automated processes or metadata updates.

Workaround I use

If users only need to read the document and rarely edit it, I set the file to be read‑only by default. This prevents SharePoint from opening the file in edit mode and avoids the locking behavior.

This thread describes a similar scenario: 

Sharepoint - Prevent a new version each time a document is read | Microsoft Community Hub

Default - "Open Read Only" for Office Files | Microsoft Community Hub

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