Microsoft fixes Teams and Outlook launch crashes on ARM Windows PCs
A bug triggered by August security updates caused productivity apps to fail on Copilot+ devices; a September patch now resolves the issue.
Microsoft has resolved a software bug that caused Microsoft Teams and the new Outlook for Windows to crash or fail to launch on ARM-based devices. The fix arrives after a period of instability for users of Windows 11 on ARM architecture.
The issue was triggered by Windows security updates released on or after August 11, 2026, specifically update KB5121003. According to Microsoft, these updates caused the two productivity applications to either close unexpectedly or fail to open entirely. The bug primarily impacted ARM-based Windows 11 devices running version 24H2, including high-profile hardware such as the Surface Pro 11 and Surface Laptop 7. Reports indicate the failure was most prevalent on new or freshly imaged PCs that had not yet installed the latest Microsoft Store updates.
A Turbulent Update Cycle
This failure occurred during a broader window of instability for Windows 11 updates throughout August 2026. During this period, other confirmed regressions emerged, including .NET Framework updates that broke printing and PDF exporting capabilities within WPF applications. These overlapping issues created a challenging environment for users transitioning to the latest Windows builds, particularly those utilizing the ARM platform.
Implications for the ARM Ecosystem
The reliability of core productivity tools is critical as Microsoft aggressively pushes its Copilot+ PC initiative. Because these devices rely heavily on ARM architecture to deliver the power efficiency and AI capabilities required for next-generation computing, any failure in essential apps like Teams and Outlook threatens enterprise adoption. For corporate IT departments, the stability of the ARM ecosystem is a prerequisite for moving away from traditional x86 hardware. When basic communication tools fail following a security patch, it undermines user trust in the viability of ARM-based Windows machines for professional workloads.
The Path to Resolution
Microsoft delivered the permanent resolution on September 8, 2026, as part of the September Patch Tuesday cumulative updates. Users can resolve the launch failures by installing update KB5124012. While the primary fix is now available, administrators are encouraged to ensure that all Microsoft Store updates are current on freshly deployed images to prevent similar conflicts. Moving forward, the industry will be watching how Microsoft manages the intersection of security patching and ARM-specific compatibility to ensure that the rollout of Copilot+ hardware remains seamless.