Backup or replication jobs with Application Aware Image-Processing enabled may fail on the server hosting Azure AD Connect Sync with an error indicating the SQL writer has failed. After the job has failed, running “Vssadmin list writers” from an administrative command prompt on the Azure AD Connect Sync server shows the sql writer in failed state. In Hyper-V, the error in the statistics window in VBR may be “guest processing skipped” or may indicate that the checkpoint has failed. In Vmware, the error is usually “Backup job failed. Cannot create a shadow copy of the volumes containing writer's data. A VSS critical writer has failed. Writer name: [SqlServerWriter]”
Updates to Azure AD Connect Sync will sometimes leave the server in a state where VSS snapshots will cause the SQL Server writer to fail.
After installing service pack 4 for sql localdb 2012 and rebooting the server (https://www.microsoft.com/en-us/download/confirmation.aspx?id=56040), the jobs will generally be able to run successfully. In some instances, the error may return after future updates to the Azure AD Connect Sync Client, in which case another reboot will resolve the issue. Microsoft has been made aware of the issue and future updates to Azure AD Connect Sync may either not cause this problem or should prompt the user for reboot. If a future update to the Azure AD Connect Sync client does not prompt for a reboot, you can either reboot proactively after updating to prevent this issue from happening or test the job and reboot if it fails following the update.