"This update may introduce system-wide issues that affect Microsoft VSS (Volume Shadow Copy Service) operations, leading to backup failures," Acronis says.
KB5083769 triggers VSS timeouts on Windows 11 24H2 and 25H2
The April 2026 security update KB5083769 has been reported to break third-party backup applications on systems running Windows 11 24H2 and 25H2 by causing Volume Shadow Copy Service (VSS) snapshots to time out. User reports, first spotted by Microsoft MVP Susan Bradley, indicate that the update causes failures where VSS cannot complete snapshot creation within expected time limits, producing a VSS service timeout.
Products and editions confirmed affected
The list of affected software includes, but is not limited to, Acronis (Cyber Protect Cloud), Macrium (Reflect), NinjaOne Backup, and UrBackup Server. Acronis published a support document confirming that the problem impacts Windows 11 Pro and Home editions and that backup operations fail with the error: "The backup has failed because Microsoft VSS has timed out during the snapshot creation." Acronis also warns that in some cases the affected machine may lose connectivity with the cloud console and appear offline.
Temporary workaround: uninstall KB5083769 and pause updates
Acronis and user reports point to an actionable, temporary mitigation. Affected users are advised to uninstall the "Security update for Microsoft Windows (KB5083769)" using the sequence Settings > Windows Update > Update history > Related settings > Uninstall updates, then pause Windows updates and reboot the system. That sequence is offered as a stopgap while the underlying issue remains unresolved.
Context from related April updates and vendor response
BleepingComputer reached out to Microsoft for more information but a response was not immediately available. The April update cycle has already required additional corrective action: earlier in the month Microsoft released out-of-band updates to fix issues affecting Windows Server systems that caused restart loops and update installation failures after installing the April 2026 security updates. Separately, Microsoft warned that some Windows Server 2025 devices will boot into BitLocker recovery and ask for a BitLocker key after installing the KB5082063 update.
How technologists, enterprises, and end users are likely to respond
- Technologists and security teams: Expect immediate inventory checks for Windows 11 24H2/25H2 endpoints running third-party backup tools that rely on VSS, followed by staged rollbacks of KB5083769 where backups fail and service continuity is at risk.
- Affected enterprises and procurement leaders: Vendors named in reports—Acronis, Macrium, NinjaOne, UrBackup—will be monitored for formal patches or guidance; procurement and IT operations teams will need to coordinate rollback actions and communications with incident response and cloud-console monitoring teams if devices appear offline.
- End users and general IT administrators: Individuals advised by vendor documentation will follow the uninstall path and pause updates, then verify backup success post-reboot. Users should also watch for loss of cloud console connectivity as noted by Acronis.
The record in April shows a security-update cycle that continues to produce operational side effects: KB5083769 has degraded a critical interoperability service (VSS) relied upon by backup suites, and Microsoft has already had to issue out-of-band server fixes and warn about BitLocker-related boot behavior from other April updates. With vendor confirmation from Acronis and multiple third-party backup vendors cited by users, the immediate steps—uninstall KB5083769, pause updates, reboot, and monitor backup and cloud-console status—are clear. What remains open is when Microsoft will provide a definitive fix or guidance; BleepingComputer's outreach to Microsoft had not yet produced a response at the time of reporting.
Original reporting: https://www.bleepingcomputer.com/news/microsoft/april-kb5083769-windows-11-update-causes-backup-software-failures/
