A Microsoft file hosting and synchronization service.
Hi zhao hai,
Welcome to Microsoft Community.
Could you confirm if the save path of one of the documents is like this: https://d.docs.live.net/Example/Documents/Filename.docx, while the other is: C:\Users\Thomas\OneDrive\Documents\Filename.docx?
If so, it is likely that OneDrive unexpectedly disconnected while you were editing the document. Please refer to this response: Two Word files with same name in recent files list - Microsoft Community
If not, kindly share more context and screenshots with me so that I can better diagnose your issue.
If you have any other questions or want to share more context, please let me know in your reply!
Best Regards,
Thomas C - MSFT | Microsoft Community Support Specialist