Microsoft’s latest Release Preview cumulative — KB5064080 (OS Build 22621.5840 / 22631.5837) — is a focused, non‑security preview update that patches a string of real‑world reliability issues across File Explorer, file sharing, and the ReFS file system while also surfacing a major enterprise capability, Windows Backup for Organizations. The release is optional (a “C” or preview release) and is intended for validation in Release Preview and pilot rings before broader distribution; Microsoft’s support notes and the Windows Insider announcement list the fix set and instruct admins to obtain the update from the Optional updates area in Windows Update. (support.microsoft.com) (blogs.windows.com)
Windows servicing continues to use parallel build families that can cause the same KB to appear with slightly different build numbers depending on the feature‑on (22631) or feature‑off (22621) branch. KB5064080 first showed up in the Release Preview Channel in mid‑August 2025 as Build 22631.5837, with a follow‑up minor release (22631.5840 / 22621.5840) addressing update‑time issues. Microsoft’s support page lists the update as a non‑security “quality” release for Windows 11, version 23H2 and provides the full itemized changelog and installation guidance. (blogs.windows.com, support.microsoft.com)
This package is deliberately not a feature release in the consumer sense. Instead, it is a reliability rollup intended to reduce helpdesk noise and operational fragility in hybrid and enterprise environments by fixing issues that cause visible productivity impacts or severe edge‑case failures. The update also contains a Servicing Stack Update (SSU) bundled with the Latest Cumulative Update (LCU); administrators should note SSUs are persistent and affect rollback options for the combined package. (support.microsoft.com)
Source: Windows Report Windows 11 Preview Update KB5064080 Fixes Key File Explorer and Sharing Issues
Background / Overview
Windows servicing continues to use parallel build families that can cause the same KB to appear with slightly different build numbers depending on the feature‑on (22631) or feature‑off (22621) branch. KB5064080 first showed up in the Release Preview Channel in mid‑August 2025 as Build 22631.5837, with a follow‑up minor release (22631.5840 / 22621.5840) addressing update‑time issues. Microsoft’s support page lists the update as a non‑security “quality” release for Windows 11, version 23H2 and provides the full itemized changelog and installation guidance. (blogs.windows.com, support.microsoft.com)This package is deliberately not a feature release in the consumer sense. Instead, it is a reliability rollup intended to reduce helpdesk noise and operational fragility in hybrid and enterprise environments by fixing issues that cause visible productivity impacts or severe edge‑case failures. The update also contains a Servicing Stack Update (SSU) bundled with the Latest Cumulative Update (LCU); administrators should note SSUs are persistent and affect rollback options for the combined package. (support.microsoft.com)
What KB5064080 fixes — headline items
The update addresses a mixture of client and server/enterprise problems. The most operationally meaningful items include:- File Explorer regressions: Explorer sometimes showed only a single folder (for example, Desktop) rather than the expected recent/recommended content, and syncing many SharePoint sites into Explorer could cause slow folder navigation and context‑menu latency. (support.microsoft.com, neowin.net)
- File sharing over QUIC: Accessing SMB shares over QUIC could intermittently suffer unexpected delays and timeouts; the update includes mitigations to reduce those latency incidents. (support.microsoft.com, neowin.net)
- ReFS stability: A race/stop‑response could occur when deduplication and compression were both enabled on ReFS volumes; that scenario is now fixed to prevent occasional system hangs. (support.microsoft.com)
- Windows Backup for Organizations: Microsoft marks the enterprise backup/restore feature as New! — generally available in the release notes, handing administrators a first‑party tool to back up and restore curated Windows settings for Entra‑joined devices via Intune. Administrators must validate tenant enablement and prerequisites before assuming full availability. (support.microsoft.com, learn.microsoft.com)
Deep dive: File Explorer — what broke, and why this fix matters
The symptoms and user impact
Several users and IT teams reported that File Explorer sometimes displayed only a single folder (commonly Desktop) on the Home/Recommended view instead of showing recent files and the expected content overview. For heavy Office/SharePoint users, mounting or syncing many SharePoint sites into Explorer could cause pronounced performance slowdowns when browsing folders, invoking the context menu (right‑click), or opening files. These behaviours manifest as immediate workflow friction — slow file open times, lag in context menus, and visible freezes — which quickly generate helpdesk calls. (support.microsoft.com, neowin.net)What the update changes
Microsoft’s changelog indicates targeted fixes that address the conditions leading Explorer to fall back to the single‑folder view and the performance regressions caused by enumerating many cloud‑backed sites. While Microsoft does not publish the exact code changes in the public KB, the fixes are scoped to Explorer’s management of recently used content and the code paths that enumerate mounted SharePoint/OneDrive locations. The net effect should be fewer Home/Recommended display issues and lower latency when large numbers of SharePoint locations are present. (blogs.windows.com, neowin.net)Practical validation for admins and power users
- Test on pilot devices that routinely mount multiple SharePoint sites. Open multiple folders, use the context menu in directories with heavy SharePoint syncing, and measure apparent delays.
- Validate the Home/Recommended pane by signing in with a user who experienced the single‑folder symptom previously, and exercise common file launch workflows.
- Capture Explorer crash/ETW traces if issues persist and involve vendor support if third‑party file system filters or cloud storage connectors are present, since they often interact with Explorer’s enumeration logic.
Deep dive: SMB over QUIC — faster, more predictable remote file access
Why SMB over QUIC matters
SMB over QUIC provides VPN‑less, secure file share access over UDP by leveraging QUIC transport. It’s a modern alternative for mobile and remote users who need access to file servers without a full network VPN, and it plays a role in zero‑trust / cloud‑forward architectures.The issue and the fix
Administrators reported unexpected delays and occasional timeouts when accessing SMB shares over QUIC. Those delays show up as slow file open times, delayed directory listings, or transient access failures. KB5064080 includes mitigations aimed at reducing those latency and timeout conditions, improving reliability for distributed users using QUIC‑based file share access. (support.microsoft.com, neowin.net)Validation checklist
- Reproduce SMB over QUIC access patterns from remote networks and measure file open latency pre‑ and post‑update.
- Test both small file operations and directory listing behavior; timeouts typically surface in directory enumeration or large read requests.
- If your deployment uses load balancers, firewalls, or proxies that observe or modify QUIC traffic, include them in tests — intermediary devices can interact poorly with QUIC flows and introduce symptoms unrelated to the OS fix.
Deep dive: ReFS deduplication + compression — fixing a server‑grade hang
The problem
Resilient File System (ReFS) is used in many server, virtualization host, and backup appliance scenarios for its data integrity and scalability features. Microsoft identified a rare condition where enabling deduplication and compression simultaneously could cause a system to become unresponsive (a stop‑response). For storage stacks that combine dedupe and compression to optimize space, that is a high‑severity operational risk. (support.microsoft.com)What KB5064080 does
The KB lists a fix for the race/hang condition that could occur when deduplication and compression were both active on ReFS volumes. The patch removes the particular interoperation failure, reducing the risk of server outages during intense dedupe/compression operations. The exact implementation details are not public, but the outcome is increased ReFS stability under those configuration combinations. (support.microsoft.com)Operational guidance
- If you operate ReFS volumes with both deduplication and compression, test the update in a lab or pilot cluster before rolling to production hosts.
- Run dedupe jobs and compressible data ingestion scenarios (e.g., large VM disk operations, backup ingest) under synthetic load to validate no hangs or performance regressions.
- Maintain tested backups and have documented recovery steps before changing storage tuning parameters; even high‑quality fixes can interact unpredictably with firmware, third‑party filter drivers, or hypervisor software.
Windows Backup for Organizations — what it is and what it isn’t
The feature in brief
KB5064080 lists Windows Backup for Organizations as “New!” and states it is generally available. The feature is intended to let organizations back up curated Windows settings at scale and restore them to Entra‑joined endpoints during enrollment or reprovisioning, thereby improving device refresh and upgrade workflows. It is administered via Microsoft Intune and tied to Microsoft Entra identity. The Intune documentation spells out prerequisites and the scoped nature of the backup (settings and environment state, not installed applications). (support.microsoft.com, learn.microsoft.com)Key constraints and realities
- Scope: The solution focuses on settings and environment state (system settings, personalization, accessibility, network and device settings), not full application or file backups. Organizations must not conflate it with full system backup solutions. (learn.microsoft.com)
- Prerequisites: Devices must be Microsoft Entra joined (hybrid or cloud‑only) and managed with Intune in the supported OS versions/builds indicated in Microsoft’s Intune documentation. Tenant enablement is required; administrators must configure the restore setting in the Intune admin center and confirm Conditional Access requirements. (learn.microsoft.com)
- Verification: The Release Preview note is a strong signal of general availability, but administrators should verify the feature’s presence and behavior in their admin portals and perform test backup/restore cycles on nonproduction devices before broad adoption. Treat this as operationally available but tenant‑gated.
Other notable fixes (brief)
- Copilot key reliability improvements: fixes an issue preventing restart after use. (support.microsoft.com)
- Removable storage policy: resolves a device management bug where blocked USB devices were not being enforced. This is important for compliance and data‑exfiltration risk mitigation. (blogs.windows.com)
- IME and Unicode rendering: fixes for extended Unicode characters (rare Chinese glyphs) and GB18030‑2022 compliance. This is meaningful for multilingual and regulated deployments. (support.microsoft.com)
- Narrator: fixes incorrect screen reader announcements in Windows Hello settings. Accessibility fixes reduce barriers for users depending on assistive technologies. (support.microsoft.com)
- Wi‑Fi reconnection after Group Policy and Remote Desktop camera enumeration: stability and peripheral reliability fixes for managed environments. (support.microsoft.com)
How to get KB5064080 and what to expect at install time
KB5064080 is an optional preview update and will not install automatically for most devices. Administrators and Release Preview Insiders can obtain it via Settings → Windows Update → Check for updates → Optional updates available, where the preview update appears. The package includes an SSU (KB5064743) bundled with the LCU; because SSUs are persistent once installed, rollback requires removing only the LCU via DISM; wusa.exe uninstall of the combined package is not supported. Follow Microsoft’s servicing guidance for SSU/LCU combined packages. (support.microsoft.com, elevenforum.com)Deployment and testing playbook (recommended)
- Pilot ring: Install KB5064080 in a small pilot group that mirrors your estate diversity (laptops, desktops, servers, ReFS hosts, VDI hosts).
- Test File Explorer scenarios: reproduce the single‑folder symptom and SharePoint heavy‑mounts; validate context menu responsiveness.
- Test SMB over QUIC: run remote file open/dir listing tests from remote networks; verify latency and timeouts are resolved. (neowin.net)
- Test ReFS operations: run deduplication and compression jobs in lab clusters under load to validate hang mitigation. (support.microsoft.com)
- Validate Windows Backup for Organizations: enable the restore setting in Intune on a lab tenant and perform a backup/restore cycle on Entra‑joined devices. Confirm what is backed up, what is not, and how restore flows work during Autopilot or enrollment. (learn.microsoft.com, support.microsoft.com)
- Monitor telemetry, event logs, and community forums for unexpected regressions; keep rollback/restore plans and golden images at the ready.
Strengths — why this update matters
- Targeted reliability: The fixes attack high‑value pain points that generate helpdesk tickets: File Explorer oddities, remote file access delays, and a potentially catastrophic ReFS hang. These are practical, operational problems rather than cosmetic issues. (support.microsoft.com, neowin.net)
- Enterprise capability: Bringing Windows Backup for Organizations to general availability (tenant gating notwithstanding) introduces a tighter first‑party option for restoring user environment settings during re‑provisioning, reducing reprovisioning time and potential desk‑side configuration work. (learn.microsoft.com, neowin.net)
- Servicing improvements: Bundling the SSU with the LCU improves installation robustness and reduces install failures, a practical win for managed deployment pipelines. (support.microsoft.com)
Risks, caveats and things to watch
- Preview nature and compatibility: KB5064080 is a Release Preview/optional package. While fixes are valuable, preview updates can still interact unpredictably with third‑party drivers, security agents (EDR/AV), and kernel‑mode filter drivers. A ringed rollout remains essential.
- SSU complicates rollback: The combined SSU+LCU package means simple wusa uninstall of the combined MSU will not remove the SSU portion. Removing the LCU requires DISM with the package name; SSUs are effectively persistent and complicate rollback strategies. Plan rollback playbooks in advance. (support.microsoft.com)
- Windows Backup for Organizations is scoped: The backup feature is not a replacement for file‑level or application backups. It’s focused on settings and environment state. Organizations must retain conventional backup systems for data, applications, and full system images. (learn.microsoft.com)
- Tenant gating and prerequisites: Even though Microsoft lists Windows Backup for Organizations as generally available in the Release Preview notes, tenant enablement, Intune configuration, and Entra join status control actual availability. Verify tenant visibility and test the workflow; do not assume instant GA availability across tenants.
- Potential for edge regressions: Past servicing cycles show that even Release Preview updates can surface new regressions on exotic hardware or bespoke stacks. Monitor community and release‑health dashboards during and after rollout.
Recommended immediate actions for IT teams
- Confirm the presence of KB5064080 in your Update management console or via Windows Update on test machines. (support.microsoft.com)
- Build a small pilot that includes: users who mount many SharePoint sites, endpoints with ReFS and dedupe/compress configs, devices that use SMB over QUIC, and devices managed by your EDR/AV stack.
- Test Windows Backup for Organizations in a lab tenant: enable the Intune restore option and perform a full backup/restore cycle to understand scope and any compliance implications. (learn.microsoft.com, neowin.net)
- Prepare rollback steps and ensure system images or other restore mechanisms are available in case you need to revert critical endpoints. Note that removing the SSU is not supported. (support.microsoft.com)
Conclusion
KB5064080 is a pragmatic preview rollup that fixes several high‑impact reliability issues across File Explorer, cloud‑backed file access, and ReFS storage, while also surfacing an important enterprise capability in Windows Backup for Organizations. For organizations that experience the reported pain points — slow Explorer behavior with many SharePoint mounts, SMB over QUIC timeouts, or ReFS dedupe/compression instability — the package is an important candidate for pilot deployment. However, because the update is optional and includes an SSU, responsible IT practice demands a staged rollout, careful testing (especially for ReFS workloads and QUIC deployments), and tenant verification before adopting the Windows Backup for Organizations feature at scale. Microsoft’s official KB and the Windows Insider notes document the changes and installation guidance; administrators should validate tenant readiness in Intune and follow staged deployment best practices. (support.microsoft.com, blogs.windows.com, learn.microsoft.com)Source: Windows Report Windows 11 Preview Update KB5064080 Fixes Key File Explorer and Sharing Issues
