Microsoft’s February 2026 cumulative update for Windows 11, known as KB5077181, has been linked in community reports to serious startup and stability issues on devices running both the 24H2 and 25H2 releases of the OS.
The update — part of Microsoft’s regular Patch Tuesday releases and intended to include security improvements and quality fixes — is reported by some users to cause systems to enter a continuous restart cycle shortly after installation. In these cases, affected PCs may reboot repeatedly — sometimes more than a dozen times — without ever successfully loading the Windows desktop.
Beyond reboot loops, users have also described login failures tied to the System Event Notification Service (SENS), where attempts to sign in fail with errors indicating that expected services cannot start. In other instances, network connectivity appears broken: machines show they are connected to a network but cannot access the internet, suggesting DHCP failures or networking stack issues after the update.
Some affected computers also display installation error codes — including 0x800f0983 and 0x800f0991 — during or after the update process, and experts point to possible mismatches in component stores or servicing processes as contributing factors.
At this time, Microsoft has not officially listed these problems as known issues for KB5077181, and the company’s documentation does not acknowledge widespread boot failures tied to the update.
Users dealing with the boot loop problem are advised to roll back the update where possible — either through the Windows recovery environment or from the “Installed Updates” view in Control Panel — and to pause automatic updates afterward to prevent the patch from reapplying until an official fix is released.
While the issue appears to impact a subset of devices rather than all installations, it underscores how complex cumulative updates — which now often combine security fixes with servicing stack changes — can sometimes introduce unintended problems on certain hardware or software configurations.
