Microsoft fixes Windows Server Active Directory sync issues

Microsoft acknowledged that September 2025 and later Windows security updates introduced a known issue on Windows Server 2025 that can cause incomplete Active Directory synchronization for large security groups (over 10,000 members) and impact Microsoft Entra Connect Sync; Microsoft published a Known Issue Rollback Group Policy, provided a registry workaround for unmanaged devices, and plans a wider fix. The advisory also notes separate update/installer and smart-card authentication issues across Windows releases and includes guidance and mitigations.