I just checked and noticed log bundle from Agent machine kb2404 has not yet uploaded and could you provide more information what have been done and fixed.
Here is the email I sent earlier for your reference.
upgraded Veeam Backup Server(VBR) to update 4b and the CBT tracking is failed for all volumes or drives. On the same backup session, Veeam Agent for Microsoft Windows will need to read all data(on the same backup job when it throw warning Failed to obtain changed block tracking map) from the backed-up volume to create incremental backup. As a result, incremental backup will require greater time. The backup is still successful with backup file created on repository.
More information on Veeam Changed Block Tracking Driver
https://helpcenter.veeam.com/docs/agentforwindows/userguide/backup_cbt_driver.html?ver=40
Moving forward, I need the Agent logs from the Agent machine for further investigation, please follow the guide below to collect the logs.
https://www.veeam.com/kb2404
In the meantime, please also ensure the Agent software CBT version is upgraded to latest version too as a result of VBR upgrade if you have not.
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Veeam Agent has been updated to version 3.0.2 on 07 Feb but the CBT driver version still stayed at driver version: 9.5.0.1307. The correct version for Veeam Agent 3.0.2 is Veeam Volume CT Driver 9.5.4.2835.
The initial reported issue is still happening on backup job dated 11 Mar where I suspect it's a known bug where this happens if C:\ volume is also a System volume (contains boot record). Hence, you should upgrade to the latest Veeam Volume CT Driver 9.5.4.2835.
Driver version
[06.02.2020 22:35:19.866] [4:8: 00] TRACE: LOAD: start.
[06.02.2020 22:35:19.866] [4:8: 00] TRACE: LOAD: OS version: 6.1 [0].
[06.02.2020 22:35:19.866] [4:8: 00] TRACE: LOAD: driver version: 9.5.0.1307.
[06.02.2020 22:35:19.866] [4:8: 00] TRACE: LOAD: build time: 10/25/17 20:13:11.
Backup job failed
[11.03.2020 00:31:43] <01> Error Invoke failed. Command: 'VeeamVolumeCt.SetUserStorePath', parameters: {(EString) DevicePath=\\?\Volume{7b4fd194-4f0a-11e1-b5f9-e4115bd3c268}; (EString) StorePath=C:\ProgramData\Veeam\EndpointData\CtStore; }. (Veeam.Backup.Common.CAgentException)
[11.03.2020 00:31:43] <01> Error at Veeam.Backup.AgentProvider.CBackupClient.OnInvokeError(Exception e, String command, CVCPCommandArgs inArgs)
[11.03.2020 00:31:43] <01> Error at Veeam.Backup.AgentProvider.CBackupClient.Invoke(String command, CVCPCommandArgs inArgs, Boolean noLog)
[11.03.2020 00:31:43] <01> Error at Veeam.Backup.AgentProvider.CBackupClient.VeeamVolumeCtSetUserStore(String devicePath, String storePath)
[11.03.2020 00:31:43] <01> Error at Veeam.EndPoint.Core.SVolumeCtDriverHelper.CanUseCtkDriver(CBackupClient client, CLiveVolumeInfo volume, CGuestDiskInfo disk, Boolean& failedToCheck)
[11.03.2020 00:31:43] <01> Error The request is not supported. (Veeam.Backup.Common.CCppComponentException)
[11.03.2020 00:31:43] <01> Error Error: in [VctSetCtStorePath] at step [5] (Veeam.Backup.Common.CCppComponentException)
[11.03.2020 00:31:43] <01> Error in c++: Error code: 0x00000032
[11.03.2020 00:31:43] <01> Error Agent failed to process method {VeeamVolumeCt.SetUserStorePath}. (Veeam.Backup.Common.CCppComponentException)
[11.03.2020 00:31:43] <01> Info
Because of the fact that the current Operating System is Windows server 2008 R2, you should either
1.) fall back to Windows default Changed Block Tracking(CBT) Mechanism as the file system use is NTFS only. All you need to do is to uninstall Veeam CBT driver version: 9.5.0.1307.
Overview of default
https://helpcenter.veeam.com/archive/agentforwindows/30/userguide/backup_cbt_default.html
Please note this is guide for install, uninstall and upgrade will appear and you need to select uninstall driver.
https://helpcenter.veeam.com/archive/backup/95u4/agents/protected_computers_driver.html
After the uninstall, you need to restart agent machine and please plan accordingly and let your customer know.
2.) upgrade the current CBT driver to version 9.5.4.2835
Please note this is guide for install, uninstall and upgrade will appear and you need to select uninstall driver.
https://helpcenter.veeam.com/archive/backup/95u4/agents/protected_computers_driver.html
After the upgrade, you need to restart the Agent machine also.
**You may also check the version installed using the same option by selecting "details" after right click the agent machine on Veeam console.
Then, you may run the backup again after perform one of the above solution. Please note that the first backup duration will take longer as a result of Veeam Agent for Microsoft Windows will need to read all data from the backed-up volume again.