Microsoft has confirmed that the April 2026 Patch Tuesday update is causing problems for many third-party backup tools on Windows 11. The update intentionally adds a specific kernel driver to the vulnerable driver blocklist for better security. Unfortunately, this change breaks Volume Shadow Copy Service functionality in several backup applications, leading to snapshot timeouts and failed backup or restore operations. Affected programs include: -Acronis Cyber Protect -Macrium Reflect -NinjaOne Backup -UrBackup, and others that rely on this driver. Microsoft recommends keeping the security update installed and contacting your backup software vendor for a compatible version that uses updated drivers. Uninstalling the patch is not advised as it leaves your system vulnerable. If your backups suddenly stopped working after the April updates, this is likely why.