Excel document should have been locked while I was working on it, another user somehow accessed the document.

When multiple users try to access an Excel document simultaneously, it can lead to conflicts, especially if the document is not set up for co-authoring. In your case, it seems that the document was not locked properly for exclusive editing, allowing another user to open it while you were still working on it. This can happen if the document is stored in a location that does not support locking, or if the Excel settings allow for multiple users to access the file without proper restrictions.

Here are some possible reasons why the other user was able to access the document while you were working on it:

1. Shared Folder Settings: If the document is stored in a shared folder that does not enforce exclusive access, multiple users may be able to open it simultaneously.
2. File Format: The file format being used might not support locking. For example, if the document is in a format that does not allow for co-authoring, it may lead to such issues.
3. Network Issues: Sometimes, network issues can prevent Excel from properly locking the document, allowing another user to access it inadvertently.
4. Excel Configuration: If the Excel settings are configured to allow multiple users to edit the document, this could also lead to the situation you experienced.

To avoid this in the future, ensure that the document is saved in a format that supports co-authoring, and check the settings of the shared folder to enforce exclusive access. Additionally, consider using a cloud-based solution that better manages concurrent access to documents.

References:

• Troubleshoot why Excel doesn't save changes

Hi @T,

Thank you for posting your question in the Microsoft Q&A forum.

According to your concern, may you confirm that is the file stored in OneDrive/SharePoint, or is it on a network/shared drive or a synced folder?

Based on your description, the workbook was likely not in an Excel co-authoring session but using traditional file locking if the Excel file is opened from a location that doesn’t fully support co-authoring (for example a network share or a synced folder). In that case, a second user can sometimes still open the file using a cached/synced copy. However, the problem is that when either user saves, Excel detects the file version has changed and the message “the file may have been changed by another user since you last saved it” appears to offer the user Saving a Copy to prevent overwriting the original file.

To avoid this, I greatly suggest storing the workbook in OneDrive or SharePoint. Then, both you and other users can open it via the shared link (or Excel for the web) using Excel for Microsoft 365, ideally with AutoSave enabled for the best co-authoring experience.

For your reference, you can find more detailed explanation about co-authoring in Excel in:

• Excel file is locked for editing - Microsoft Support
• How to troubleshoot errors when you save Excel workbooks - Microsoft 365 Apps | Microsoft Learn
• Document collaboration and co-authoring - Microsoft Support

I hope this helps you move forward smoothly. If you have any questions or need further assistance, please feel free to share them in the comments on this post so I can continue to support you.  

Thank you for your patience and understanding. Looking forward to your response.

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