Delta Migration Misses Recently Changed Files: OneDrive for Business Fix

When you run a delta migration from a source platform to OneDrive for Business, some recently changed files do not transfer. This typically happens because the delta migration tool scans the source based on a snapshot or timestamp that does not include changes made during the final hours before the cutover. The result is missing files that were modified, renamed, or created after the last delta scan. This article explains why delta migrations miss recent file changes and provides a reliable method to locate and sync those files to OneDrive for Business.

Why Delta Migration Misses Recently Changed Files

Delta migration in OneDrive for Business uses a timestamp-based scan to identify files that changed since the last full migration. The tool records the last modified date of each file and compares it to the delta start time. Any file whose last modified date falls after the delta scan completes is not included in the transfer. This gap occurs for several reasons.

Delta Scan Timing

The delta migration process runs on a schedule. If a file is modified after the delta scan begins but before the scan finishes, the tool might not detect it. In a busy environment where users are actively working, files can change every few seconds. A delta scan that takes 10 minutes to run will miss any file saved during that window.

Source System Latency

Some source platforms, such as on-premises file servers or third-party cloud storage, do not update the last modified timestamp immediately. A file can be saved, but the metadata on the source might reflect an earlier time. The delta migration tool reads that timestamp and skips the file, believing it has not changed.

File Rename or Move During Migration

If a user renames or moves a file while the delta migration is running, the tool may see the original path as unchanged and the new path as a new file that does not match any delta filter. The result is a file that exists on the source but never appears in the destination OneDrive folder.

Steps to Locate and Sync Missed Files to OneDrive for Business

The fix involves identifying which files were missed and then performing a targeted sync using either the OneDrive sync app or the SharePoint Migration Tool. Follow these steps in order.

1. Run a file comparison report between source and destination
   Use a tool like Microsoft Migration Manager or a third-party comparison utility. Export a list of all files from the source folder and compare it to the file list in the target OneDrive folder. Look for files that exist on the source but are missing in the destination. Focus on files with a last modified date that falls within the last 48 hours before and after the delta migration run.
2. Identify the delta migration timestamp from the migration log
   Open the migration report provided by your migration tool. Look for the column labeled “Delta Start Time” or “Last Delta Scan.” Write down the exact UTC timestamp. Any file with a last modified date after this timestamp is a candidate for the missed file list.
3. Manually copy missed files using the OneDrive sync app
   On the computer where the source folder is accessible, open File Explorer. Navigate to the source folder. Select all files whose last modified date is after the delta timestamp. Press Ctrl+C to copy them. Open the target OneDrive folder in File Explorer. Press Ctrl+V to paste the files. The OneDrive sync app detects the new files and uploads them. Wait for the sync icon to show a green check mark.
4. Run a secondary delta pass with an extended date range
   If you are using the SharePoint Migration Tool SPMT, open the SPMT dashboard. Select the migration job that completed. Click “Run Again” and choose “Delta Migration.” In the advanced settings, set the delta start date to 72 hours before the original delta run. This forces SPMT to re-scan files that were modified during that extended window. Run the delta pass. Check the job results for any newly transferred files.
5. Verify file integrity in OneDrive
   Open the OneDrive folder in File Explorer. Right-click the folder and select “Check for updates” in the sync app context menu. Wait for the sync status to show “Up to date.” Open a few of the recently copied files to confirm they open correctly.

If the Migration Still Misses Files

Files are missing but the sync app shows no errors

The sync app might have skipped files due to file name length or invalid characters. Open the source folder. Check for file names that exceed 400 characters or contain characters like ~ " # % & : < > ? / \ |. Rename those files on the source to remove invalid characters. Copy them again to the OneDrive folder.

OneDrive sync app stops responding after pasting many files

Pasting hundreds of files at once can overload the sync engine. Instead, paste files in batches of 50 or fewer. Wait for each batch to finish syncing before pasting the next batch. You can check sync progress by clicking the OneDrive cloud icon in the system tray.

Delta migration tool fails to recognize files with modified timestamps

Some source systems use a different timestamp format or do not update the last modified date for metadata-only changes. In this case, use a file hash comparison tool such as PowerShell Get-FileHash. Run Get-FileHash -Path "C:\source\" -Algorithm MD5 | Export-Csv source_hashes.csv on the source and the same command on the destination. Compare the hash values. Files with matching hashes do not need to be re-copied. Files with mismatched hashes are the ones that changed and should be copied manually.

Delta Migration vs Full Migration: Key Differences

Item	Delta Migration	Full Migration
Description	Transfers only files that changed since the last scan	Transfers all files from the source to the destination
Speed	Fast, because only modified files are processed	Slow, because every file is scanned and transferred
Risk of missing recent changes	High, due to timestamp cutoff	Low, because every file is examined
Best use case	Incremental updates after an initial full migration	Initial bulk transfer or final cutover with zero tolerance for missing files

Delta migration is an efficient way to keep OneDrive files in sync after the first bulk transfer. But its reliance on timestamps means files changed during the delta window are missed. A full migration at cutover time eliminates this gap entirely. If your migration timeline allows, schedule a final full migration pass immediately before the cutover deadline.

You can now identify which files were missed during a delta migration and sync them to OneDrive for Business using either the manual copy method or an extended delta pass with SPMT. For large file sets, run a file hash comparison to confirm that no content was skipped. As an advanced tip, schedule your delta runs during off-peak hours and set the delta start time to 24 hours before the actual scan to create a buffer that captures late changes.