Microsoft has acknowledged a significant issue affecting Windows Server 2025 systems, particularly after the installation of the October 2025 security updates. This issue disrupts Active Directory directory synchronization, especially impacting organizations with large security groups exceeding 10,000 members. The synchronization failures affect applications relying on DirSync for on-premises Active Directory Domain Services and particularly impact those using Microsoft Entra Connect Sync to link on-premises directories with cloud services. The problem was first noted on October 14, 2025, after the installation of the September 2025 Windows security update (KB5065426). A temporary workaround involves modifying the Windows registry by creating a DWORD value named 2362988687 with a value of 0 under the FeatureManagement Overrides section at HKEYLOCALMACHINE. Microsoft cautions that incorrect registry changes can lead to severe complications. There is no definitive timeline for a permanent fix, and the issue is limited to Windows Server 2025, with no similar problems reported for earlier server editions or client versions of Windows. Organizations using Windows Server 2022 or older are unaffected. Administrators should assess synchronization needs before deploying the October 2025 updates and monitor for updates regarding a permanent resolution.