Microsoft has pushed a targeted Release Preview update identified as KB5064080 into the Windows 11 servicing stream, delivering incremental reliability fixes across File Explorer, storage (ReFS), networking (SMB over QUIC), input/IME handling, device‑management policy enforcement and more — and it surfaces Windows Backup for Organizations as a new enterprise‑facing capability to watch. (blogs.windows.com) (neowin.net)
Windows 11 servicing continues to use parallel build families — the 22621 family (feature-off) and the 22631 family (feature-on) — so the same KB can appear with slightly different OS build identifiers depending on the build family and minor follow‑ups. The KB5064080 flight first appeared to Release Preview Insiders as Build 22631.5837, and Microsoft subsequently published a small follow‑up that moved the package to Build 22631.5840 to address update‑time issues; variants for the 22621 branch are handled in the same KB lineage for feature‑off systems. (blogs.windows.com) (elevenforum.com)
This release is explicitly framed as a quality and reliability package rather than a major consumer feature push. It’s distributed via the Release Preview channel for Windows Insiders and will be the preview/optional precursor for the fixes that may later roll into broader cumulative updates. Because preview updates do not carry mandatory security patches (those arrive on Patch Tuesday), their primary role is to let Microsoft and the community validate fixes before wider production delivery. (blogs.windows.com)
For organizations, two fixes are particularly material:
Caveat and caution: community posts also demonstrate that preview updates occasionally interact unpredictably with specific drivers, vendor storage stacks and endpoint protection agents; communities reported regressions for prior preview flights (some serious), reinforcing that preview builds should be validated in pilot rings prior to broader deployment. Those community signals do not contradict Microsoft’s changelog, but they are essential operational context for administrators.
Administrators should pay particular attention to:
Source: Microsoft Support August 26, 2025—KB5064080 (OS Build 22621.5840) Preview - Microsoft Support
Background / Overview
Windows 11 servicing continues to use parallel build families — the 22621 family (feature-off) and the 22631 family (feature-on) — so the same KB can appear with slightly different OS build identifiers depending on the build family and minor follow‑ups. The KB5064080 flight first appeared to Release Preview Insiders as Build 22631.5837, and Microsoft subsequently published a small follow‑up that moved the package to Build 22631.5840 to address update‑time issues; variants for the 22621 branch are handled in the same KB lineage for feature‑off systems. (blogs.windows.com) (elevenforum.com)This release is explicitly framed as a quality and reliability package rather than a major consumer feature push. It’s distributed via the Release Preview channel for Windows Insiders and will be the preview/optional precursor for the fixes that may later roll into broader cumulative updates. Because preview updates do not carry mandatory security patches (those arrive on Patch Tuesday), their primary role is to let Microsoft and the community validate fixes before wider production delivery. (blogs.windows.com)
What’s in KB5064080 — the short list
The official Windows Insider announcement and corroborating industry coverage highlight the package’s scope. Major items include:- File Explorer: Fixes where Explorer could unexpectedly show only a single folder (e.g., Desktop) and performance slowdowns when many SharePoint sites are synced into Explorer. (blogs.windows.com) (neowin.net)
- Device management: Repair for a policy enforcement bug that could allow removable storage (USB drives, memory sticks) to not be properly blocked. (blogs.windows.com)
- File sharing (SMB over QUIC): Mitigations for timeouts and unexpected delays when accessing SMB shares over QUIC. (neowin.net)
- File system (ReFS): A critical fix for a rare condition where enabling de‑duplication and compression together on ReFS volumes could cause the system to stop responding. (neowin.net)
- Input / IME and localization: Fixes for extended Unicode characters (including some rare Chinese symbols) rendering as blank or incorrect glyphs, and an IME issue that produced empty boxes for certain characters; includes GB18030‑2022 compliance adjustments. (neowin.net)
- Narrator / Accessibility: Corrected narration of a Windows Hello checkbox label in Narrator. (blogs.windows.com)
- Network connectivity: Fix so Wi‑Fi will reconnect automatically after Group Policy updates in affected scenarios. (neowin.net)
- Remote Desktop: Camera enumeration fixes so cameras added/removed during RDS sessions appear correctly. (neowin.net)
- Windows Backup for Organizations: Listed as “New!” in the release notes — Microsoft indicates broader availability for the enterprise backup/restore capability, though tenant enablement and prerequisites must be validated before assuming GA in your environment. (neowin.net)
Why this matters: practical impact for users and IT pros
Short, visible regressions like File Explorer showing incomplete content or performance degradation when syncing many SharePoint sites are immediate productivity killers in hybrid workplaces. Explorer bugs show up across desktops and laptops and are among the first issues users complain about. Fixing these reduces noise for help desks and improves daily workflows. (neowin.net)For organizations, two fixes are particularly material:
- Removable storage policy enforcement: If an endpoint policy reports that removable media is blocked but the OS fails to enforce it, organizations are exposed to data exfiltration and compliance risk. This KB explicitly addresses that enforcement gap. (blogs.windows.com)
- ReFS deduplication + compression hang: ReFS is commonly used on file servers, virtualization hosts and backup appliances. The combination of de‑duplication and compression is used in storage optimization scenarios; a condition that can cause stop responses is a high‑severity operational risk for any system using ReFS. The fix here reduces the chance of server outages during heavy dedupe/compression operations. (neowin.net)
Verification and cross‑checks
Microsoft’s Windows Insider blog documents the official changelog for the Release Preview build, which is the authoritative source for the items above. Independent industry outlets (Neowin, forum communities) reproduced and expanded the log, and community threads tracked a subsequent small update that moved the package to Build 22631.5840 to correct update‑time issues. These independent echoes corroborate the main technical claims in Microsoft’s announcement. (blogs.windows.com) (neowin.net) (elevenforum.com)Caveat and caution: community posts also demonstrate that preview updates occasionally interact unpredictably with specific drivers, vendor storage stacks and endpoint protection agents; communities reported regressions for prior preview flights (some serious), reinforcing that preview builds should be validated in pilot rings prior to broader deployment. Those community signals do not contradict Microsoft’s changelog, but they are essential operational context for administrators.
Installation, rollout and testing guidance — recommended checklist
Organizations should approach KB5064080 the same way they would any Release Preview/optional update: pilot, validate, then expand. The following checklist is pragmatic and prioritized:- Identify pilot cohort
- Include representative device types: consumer laptops, corporate managed laptops, servers using ReFS, devices that use SMB over QUIC, and endpoints that exercise Family Safety or removable storage policies.
- Backup and recovery readiness
- Ensure image backups or restore points exist for pilot devices. Confirm you can uninstall or roll back updates where applicable (be aware that packages containing SSUs require DISM operations to remove).
- Validate Windows Backup for Organizations
- Check your Intune/admin portals for the Windows Backup for Organizations capability and run at least one full backup and restore cycle in a test tenant to verify scope, prerequisites and what settings are included before enabling broadly. Do not assume immediate GA for your tenant without verification.
- Storage and ReFS tests
- For ReFS hosts, run dedupe + compression jobs in a controlled test cluster. Validate backup/restore workflows, VSS behavior and reboot cycles. Coordinate with storage vendor guidance if you use OEM drivers or filters.
- File Explorer / SharePoint heavy loads
- Exercise scenarios where users mount many SharePoint or OneDrive sites to simulate context‑menu and navigation workloads. Monitor explorer.exe crashes, hangs, and responsiveness. (neowin.net)
- SMB over QUIC and RDS camera tests
- Test remote file access over QUIC for timeouts and latency. For RDS deployments, test camera hot‑plugging during sessions and verify that newly attached devices enumerate correctly. (neowin.net)
- Policy and Wi‑Fi resiliency tests
- Apply Group Policy updates and confirm Wi‑Fi reconnect behavior. Verify removable media policy enforcement across endpoint security stacks (EDR/AV agents) to confirm third‑party interactions. (blogs.windows.com)
- Telemetry and monitoring
- Monitor application crash rates, kernel bugchecks, Windows Update health telemetry and helpdesk tickets during the pilot phase. Maintain a rollback plan with step‑by‑step procedures and required command lines for uninstalling cumulative updates where possible.
Known risks and compatibility considerations
- Third‑party drivers and security agents: Historically, even Release Preview updates can interact negatively with vendor drivers and Enterprise EDR/AV agents. Expect variability by OEM and security vendor. Pilot accordingly and gather vendor compatibility statements when applicable.
- ReFS and storage vendors: The ReFS dedupe/compression fix addresses a severe hang scenario, but the underlying environment (hardware RAID controllers, vendor dedupe engines, storage filter drivers) can introduce edge cases. Test with vendor‑supplied firmware and driver versions.
- SSU packaging nuance: Microsoft has been bundling Servicing Stack Updates (SSU) with LCUs to simplify installation. That approach reduces sequencing failures but also makes simple uninstall operations less straightforward — SSUs are not removable in the usual way and require DISM-level operations to address. Plan for that in your rollback documentation.
- Preview vs. mandatory security updates: Preview updates are optional and do not replace Patch Tuesday security updates. They are useful for early validation but skipping them does not leave you unpatched for critical CVEs that Microsoft releases during Patch Tuesday. Use previews only where the fixes are relevant to active pain points you need addressed earlier.
- Windows Backup for Organizations readiness: The release notes’ "New!" marker is meaningful but not a guarantee of immediate availability for every tenant. Admins must validate prerequisites (Intune, Entra permissions, licensing) and confirm which categories of data/settings the service includes. Treat it as a managed rollout requiring verification.
Known community reports and historical context
Community archives and support forums show that preview updates can produce a range of outcomes in the wild — from flawless installs to regressions that require system restore or full reinstalls. Recent months’ preview flights produced a small number of high‑impact reports (Wi‑Fi, RDP black screens, restore point deletions) that required community troubleshooting and, in some cases, Microsoft follow‑ups. These reports underscore the operational reality of preview builds: they’re a valuable early look but not a substitute for a disciplined ring‑based rollout in production.Administrators should pay particular attention to:
- Early reports that preview updates occasionally remove restore points or affect system restore behaviors (this has appeared in community threads for other preview flights). Confirm that your backup strategy does not rely solely on in‑place restore points when testing previews.
- Reports of networking regressions on specific NIC chipsets after earlier previews; if you manage a fleet that uses a narrow set of hardware, include that hardware in the pilot ring.
Step‑by‑step: How to get KB5064080 (if you choose to test)
- On a test device enrolled in the Release Preview channel, open Settings → Windows Update → Check for updates.
- Look for the optional preview entry labeled KB5064080 (it may appear with the build suffix that matches your device’s family: 22621.xxxx or 22631.xxxx). (blogs.windows.com)
- Download and install the update, then reboot when prompted. If you need to remove the package and it contains an SSU, follow Microsoft’s DISM removal guidance for combined packages.
Critical analysis — strengths, weaknesses and operational risk
Strengths- Targeted reliability work: The KB demonstrates Microsoft’s focus on solving high‑impact nuisances that translate to fewer helpdesk calls (Explorer, Family Safety, removable storage policy). These are pragmatic fixes that improve day‑to‑day experience. (neowin.net)
- Enterprise‑grade storage fix: The ReFS fix addresses a rare but severe hang condition, which is the kind of stability investment that matters for servers, backup hosts and virtualization infrastructures. (neowin.net)
- Strategic enterprise capability: Listing Windows Backup for Organizations as “New!” signals an important push toward first‑party organizational backup/restore tooling — a meaningful capability if and when tenant enablement is complete.
- Preview volatility: Preview updates are inherently less battle‑tested than Patch Tuesday LCUs; community history shows previews can regress in specific hardware/driver combinations. That volatility elevates operational risk if the update is pushed broadly without pilot validation.
- Packaging complexity: Combined SSU + LCU packaging reduces installation failures but complicates uninstalls and forensic rollback actions. This increases the operational burden on help desks when post‑update actions are needed.
- Unclear tenant availability: Windows Backup for Organizations’ appearance in Release Preview notes does not equal immediate tenant‑wide GA; administrators must validate prerequisites and scope before relying on it as a production backup strategy. Treat the claim as conditional until confirmed in your environment.
Recommended action plan for IT teams (concise)
- Short term (days): Deploy KB5064080 to a small pilot group that represents your hardware, storage and security stack diversity. Run the explicit tests (ReFS dedupe + compression, SMB over QUIC, SharePoint/Explorer heavy loads, removable storage enforcement).
- Medium term (1–3 weeks): Expand to a wider validation ring if pilot telemetry shows no regressions. Validate Windows Backup for Organizations in a lab tenant before enabling for broad provisioning.
- Long term: Incorporate the update into your standard patch cadence once you have vendor compatibility confirmations for critical drivers and the backup service’s scope is confirmed in your tenant. Maintain rollback playbooks that account for combined SSU+LCU packages.
Conclusion
KB5064080 is a pragmatic Release Preview update that addresses multiple user‑facing and enterprise scenarios — from File Explorer quirks and SharePoint sync slowdowns to a serious ReFS stability fix and a notable enterprise capability in Windows Backup for Organizations. For Windows enthusiasts and IT teams, the update reduces a set of tangible pain points and surfaces a strategic backup tool. However, because this is a preview flight and because preview updates have historically interacted unpredictably with certain third‑party drivers and management agents, the recommended path is a disciplined, ring‑based rollout: pilot, validate, then broaden. Confirm tenant readiness for Windows Backup for Organizations and validate removal/rollback procedures before widespread deployment. (blogs.windows.com) (neowin.net)Source: Microsoft Support August 26, 2025—KB5064080 (OS Build 22621.5840) Preview - Microsoft Support