KB4874 release notes and known issues

Summary

How to Identify and Repair Files That Cannot Be Opened After Restore KB ID: 4874 Product: Veeam Backup for Microsoft 365 | 8 Published: 2026-06-29 Last Modified: 2026-09-17 Updated for Veeam Backup for Microsoft 365 8.6 This article has been updated to document new Integrity Check capabilities included with Veeam Backup for Microsoft 365 8.6 . The integrity check can now process JET-based repositories and immutable repositories. Customers who ran an Integrity Check while running Veeam Backup for Microsoft 365 8.5, are advised to upgrade to version 8.6 and run the Integrity Check again. Purpose This article provides steps to identify and repair SharePoint, OneDrive, Teams files, and list attachments that were backed up with corrupted content due to the issue described in KB4835 . Solution Before You Begin Ensure you’re running Veeam Backup for Microsoft 365 version 8.5 or later before proceeding. When the Integrity Check is performed on an object storage repository, there will be a temporary increase in the number of API calls the storage system handles while previously written files are scanned for inconsistencies. The redownloading of affected files afterward also increases storage usage on that same repository. Repair Procedure The following steps are to be completed for each repository that contains SharePoint, OneDrive, and Teams files. The steps in this section use PowerShell commands that reference variables defined in one step and used in later steps, so all 5 steps should be completed sequentially for each repository. In Veeam Backup for Microsoft 365 8.5, this procedure only supports non-immutable object storage repositories. In version 8.6 and later, support for immutable object storage repositories and JET-based repositories was added. Step 1: Run an Integrity Check Open Veeam Backup for Microsoft 365 . In the main menu ( ☰ ) , expand Console , and select PowerShell . Note: Launching PowerShell from outside Veeam Backup for Microsoft 365 may require manual loading of PowerShell modules . In the PowerShell console, run the following command to import the module used by this article: This DLL module must be loaded directly to ensure the Start-VBORepositoryRepairSession cmdlet is available. Import-Module "C:\Program Files\Veeam\Backup365\Veeam.Archiver.PowerShell.dll" Copy Run the following cmdlet for the repository being investigated: $repository = Get-VBORepository - Name "Repository Name" Test-VBORepository - Repository $repository Copy Step 2: Review the Results If the Test-VBORepository output contains any of the following messages, proceed to Step 3: For Veeam Backup for Microsoft 365 8.5 The following site has corrupted file data The following list contains items referencing corrupted files For Veeam Backup for Microsoft 365 8.6 The following site has inconsistent file data The following list contains items referencing inconsistent files WARNING: The following list contains items that reference files with incomplete downloads If no messages appear, no further action is required for that repository. If you see messages other than those listed above, please contact Veeam Technical Support for assistance in investigating further. Step 3: Scan Repository and Flag Affected Items Run the following cmdlet to scan the repository and flag the affected items for re-backup. Their correct content will be redownloaded during the next backup job run in Step 4. Note that during scanning, the repository remains locked for any other operations, including backups, restores, and management. All backup and restore sessions related to this repository must be stopped before running a repair session. For an object storage repository : $session = Start-VBORepositoryRepairSession - Repository $repository - Type CleanMissingFilesData - Mode Full - Scope Full Copy For a JET-based repository (Veeam Backup for Microsoft 365 8.6+ Only): $session = Start-VBORepositoryRepairSession - Repository $repository - Type CleanMissingFilesData - Mode F

Improvements and security content

• How to Identify and Repair Files That Cannot Be Opened After Restore KB ID: 4874 Product: Veeam Backup for Microsoft 365 | 8 Published: 2026-06-29 Last Modified: 2026-09-17 Updated for Veeam Backup for Microsoft 365 8.6 This article has been updated to document new Integrity Check capabilities included with Veeam Backup for Microsoft 365 8.6 . The integrity check can now process JET-based repositories and immutable repositories. Customers who ran an Integrity Check while running Veeam Backup for Microsoft 365 8.5, are advised to upgrade to version 8.6 and run the Integrity Check again. Purpose This article provides steps to identify and repair SharePoint, OneDrive, Teams files, and list attachments that were backed up with corrupted content due to the issue described in KB4835 . Solution Before You Begin Ensure you’re running Veeam Backup for Microsoft 365 version 8.5 or later before proceeding. When the Integrity Check is performed on an object storage repository, there will be a temporary increase in the number of API calls the storage system handles while previously written files are scanned for inconsistencies. The redownloading of affected files afterward also increases storage usage on that same repository. Repair Procedure The following steps are to be completed for each repository that contains SharePoint, OneDrive, and Teams files. The steps in this section use PowerShell commands that reference variables defined in one step and used in later steps, so all 5 steps should be completed sequentially for each repository. In Veeam Backup for Microsoft 365 8.5, this procedure only supports non-immutable object storage repositories. In version 8.6 and later, support for immutable object storage repositories and JET-based repositories was added. Step 1: Run an Integrity Check Open Veeam Backup for Microsoft 365 . In the main menu ( ☰ ) , expand Console , and select PowerShell . Note: Launching PowerShell from outside Veeam Backup for Microsoft 365 may require manual loading of PowerShell modules . In the PowerShell console, run the following command to import the module used by this article: This DLL module must be loaded directly to ensure the Start-VBORepositoryRepairSession cmdlet is available. Import-Module "C:\Program Files\Veeam\Backup365\Veeam.Archiver.PowerShell.dll" Copy Run the following cmdlet for the repository being investigated: $repository = Get-VBORepository - Name "Repository Name" Test-VBORepository - Repository $repository Copy Step 2: Review the Results If the Test-VBORepository output contains any of the following messages, proceed to Step 3: For Veeam Backup for Microsoft 365 8.5 The following site has corrupted file data The following list contains items referencing corrupted files For Veeam Backup for Microsoft 365 8.6 The following site has inconsistent file data The following list contains items referencing inconsistent files WARNING: The following list contains items that reference files with incomplete downloads If no messages appear, no further action is required for that repository. If you see messages other than those listed above, please contact Veeam Technical Support for assistance in investigating further. Step 3: Scan Repository and Flag Affected Items Run the following cmdlet to scan the repository and flag the affected items for re-backup. Their correct content will be redownloaded during the next backup job run in Step 4. Note that during scanning, the repository remains locked for any other operations, including backups, restores, and management. All backup and restore sessions related to this repository must be stopped before running a repair session. For an object storage repository : $session = Start-VBORepositoryRepairSession - Repository $repository - Type CleanMissingFilesData - Mode Full - Scope Full Copy For a JET-based repository (Veeam Backup for Microsoft 365 8.6+ Only): $session = Start-VBORepositoryRepairSession - Repository $repository - Type CleanMissingFilesData - Mode F

Affected products and versions

Recommended action

Review the official publisher document before deployment.

Official publisher evidence