Remote users migrating files from a file server to OneDrive for Business often discover that some files do not appear in the target location after the migration completes. This problem typically occurs because the migration tool cannot access files that are exclusively locked by a user’s local application, because file paths exceed the 400-character limit, or because the remote user’s internet connection drops during the upload. This article explains the root causes of missing files during a file server migration for remote users and provides a structured troubleshooting process to identify and recover the affected items.
Key Takeaways: Troubleshooting Missing Files in OneDrive Migrations
- Migration tool error log (e.g., Microsoft 365 Migration Manager logs): Shows each file that failed to upload and the specific failure reason, such as file lock or path length.
- OneDrive sync client > Settings > Account > Choose folders: Lets you verify that all migrated folders are selected for sync on the remote user’s device.
- Windows File Explorer > File properties > Security tab: Confirms that the user has Full Control or Modify permissions on the source file to avoid access-denied uploads.
Why Files Are Missing After a File Server Migration to OneDrive for Remote Users
When you migrate files from a file server to OneDrive for Business, the migration tool copies each file from the source location to the target OneDrive folder. For remote users, the tool runs on the user’s local machine or through a cloud-based migration service. Files can be missing for three primary technical reasons:
File Locks from Open Applications
If a remote user has a file open in an application such as Microsoft Excel, Adobe Acrobat, or a legacy line-of-business program, the operating system places an exclusive lock on that file. The migration tool cannot read a locked file and skips it without generating an error that the user sees immediately. The file is simply not uploaded.
File Path Length Exceeds 400 Characters
OneDrive for Business supports a maximum file path length of 400 characters including the file name. File server paths often include deep folder structures that push the total path over this limit. When the migration tool encounters a file with a path longer than 400 characters, it fails to upload the file and logs a path-length error.
Intermittent Network Disconnections
Remote users connect to the internet through VPNs, home broadband, or public Wi-Fi. A brief network interruption during the upload of a large file can cause the migration tool to mark that file as failed. The tool may not retry the upload automatically, leaving the file missing from the destination.
Incorrect Folder Mapping in the Migration Tool
When you configure the migration mapping, you specify which file server folder maps to which OneDrive folder. A typo in the folder name or a mismatch in the folder path causes the tool to skip the entire source folder. No files from that folder appear in OneDrive.
Steps to Identify and Recover Missing Files After Migration
Follow these steps in order to locate the missing files and upload them to OneDrive.
- Review the migration tool error log
Open the migration tool you used, such as Microsoft 365 Migration Manager, ShareGate, or Mover. Locate the error log or migration report. Filter the log for entries with status Failed or Skipped. Note the file name, folder path, and failure reason for each missing file. Common failure reasons include FileLocked, PathTooLong, AccessDenied, and NetworkError. - Check file permissions on the source file server
On the file server, right-click the folder that contains the missing files and select Properties. Go to the Security tab. Select the user account that the migration tool used to access the files. Confirm that the account has at least Read & execute and List folder contents permissions. If the account lacks these permissions, add them and rerun the migration for that folder. - Resolve file locks by closing applications
Ask the remote user to close all applications that might have files open, especially Microsoft Office apps, PDF readers, and any custom business software. Use the Computer Management console on the user’s machine, go to System Tools > Shared Folders > Open Files, and verify that no files from the migration source are listed. If a file remains locked, restart the user’s machine to release all locks. - Shorten file paths that exceed 400 characters
For each file listed with a path-length error, open the source folder in File Explorer. Rename the file to a shorter name, or move it to a shallower folder in the file server structure. Ensure the total path length including the file name is 400 characters or fewer. After shortening the path, rerun the migration for that file or folder. - Rerun the migration for failed items only
In the migration tool, select the option to retry only the failed or skipped items. Most tools have a Retry failed or Resume button. Do not rerun the entire migration because that would re-upload already successful files and waste bandwidth. After the retry completes, check the log again to confirm that the files now appear in OneDrive. - Verify that the files are syncing on the remote user’s device
On the remote user’s machine, open OneDrive settings by right-clicking the OneDrive cloud icon in the system tray and selecting Settings. Go to the Account tab and click Choose folders. Make sure the check box next to each migrated folder is selected. If a folder is unchecked, the files in it will not sync to that device. Click OK to start syncing any newly selected folders. - Use the OneDrive web interface to confirm file presence
Open a browser, sign in to https://onedrive.live.com, and navigate to the target folder. Compare the list of files in OneDrive with the list of files in the source file server folder. If a file is still missing, repeat step 1 and check the log for new errors.
If OneDrive Still Has Missing Files After the Main Fix
When the standard retry process does not recover all files, check these additional failure patterns.
OneDrive migration reports file name contains invalid characters
OneDrive does not allow files or folders that contain the characters \ / : ? " < > | or that end with a period or space. If the source file server has files with these characters, the migration tool skips them. To fix this, rename the source files to remove or replace the invalid characters. For example, replace a colon with a hyphen. After renaming, rerun the migration for those files.
OneDrive shows a duplicate file with a different name
If the migration tool uploaded a file with a slightly different name, such as Report (1).xlsx instead of Report.xlsx, the original file might have been renamed during a previous migration attempt. Check the Version history in OneDrive by selecting the file, clicking the three dots, and choosing Version history. If the correct version exists there, restore it. Otherwise, upload the original file manually from the file server.
OneDrive folder structure is incomplete
If an entire subfolder is missing from OneDrive, the folder mapping in the migration tool was incorrect. Open the migration tool and review the mapping table. Compare the source folder path with the target OneDrive folder path. Correct any mismatches and run the migration again for that folder.
Migration Tool Log Review vs Manual File Comparison: Key Differences
| Item | Migration Tool Log Review | Manual File Comparison |
|---|---|---|
| Description | Examines the migration tool’s error log to identify failed files and their reasons | Compares the file list from the source file server with the file list in OneDrive using a script or manually |
| Speed | Fast for large migrations with many files | Slow for large migrations because each folder must be examined individually |
| Accuracy | Shows exact failure reason for each file | Shows only that a file is missing, not why it failed |
| Best for | Identifying locked files, path-length errors, and permission issues | Verifying that all files from a small folder set are present |
| Tool required | Migration tool’s built-in log viewer | File Explorer, PowerShell, or a file comparison utility |
After you complete the log review and manual comparison, you will have a complete list of missing files and the reason each file failed. Use the retry steps in the previous section to upload each file.
You can now locate and recover files that were missed during a file server migration to OneDrive for Business for remote users. Next, run a full migration report after each retry to confirm that no files remain in the failed state. As an advanced tip, use the Microsoft 365 Migration Manager’s bulk error export feature to download the failure list as a CSV file, which lets you sort and filter failed items by reason and fix them in batches.