Microsoft admits Windows 11's biggest September update is breaking multiple features, days after it warned users not to delay updates

Key Points:

• Windows 11 KB5124008, released as a mandatory September 8 update, restored some Windows 10 features but is causing multiple issues including broken WSL-based apps, Remote Desktop instability, File History backup failures, Explorer.exe crashes, and GPU problems on some AMD systems.
• The update breaks apps using HCS-managed Linux VMs with Plan9 shared folders, notably affecting Anthropic’s Claude Cowork, which can no longer access local files, with Microsoft acknowledging the bug but offering no immediate fix.
• Remote Desktop Services (RDS) is unstable or unusable for many users after the update, causing frequent connection failures and sign-in problems, with Microsoft advising affected users to contact support or await future patches.
• Explorer.exe crashes, leading to black screens and unusable desktops, are primarily reported in virtual desktop environments using profile containers like Citrix UPM and FSLogix; Microsoft is investigating but requires more data to identify the root cause.
• File History backups fail to detect external drives after the update, and some AMD Radeon GPU users experience driver timeouts and system freezes; while uninstalling the update resolves some issues, Microsoft stresses the update’s critical security importance and advises caution before removal.