My Windows 11 backup broke after KB5083769 — Microsoft says this simple fix might save your files
Microsoft’s latest Windows 11 security update, KB5083769, released on April 14, 2026, has inadvertently broken backup functionality for many users. The update, Build 26200.8246, introduces enhanced security measures through changes to the psmounterex.sys driver and adds known vulnerable kernel drivers to a system blocklist to strengthen overall security.
While designed to improve system security, the update’s new behavior is causing third-party backup solutions to fail. Microsoft has acknowledged the issue publicly but maintains that this is not a bug in the operating system itself. Instead, the company recommends that affected users update their backup software to be compatible with the new security mechanisms introduced by the update.
Users experiencing backup failures after installing KB5083769 are advised to check with their backup software vendors for updated versions that support the new security features, rather than rolling back the Windows update.