Windows 11 Insider Canary Build 27943: HDR Fix, Temp Files Scan, and UI polish

Microsoft’s latest Canary-channel flight, Windows 11 Insider Preview Build 27943, is a compact but consequential maintenance update that repairs a handful of user-facing regressions — most notably a stuck Temporary files scan in Settings and an HDR toggle that would mysteriously disable itself — while leaving two high‑risk known issues (install rollbacks and an Arm64 kernel regression) on the books for Insiders to weigh before upgrading.

Background​

Canary-channel builds are the earliest public builds Microsoft ships to Insiders: experimental, fast-moving, and primarily intended for plumbing-level changes, early experiments, and triage of regressions that would be costly to push downstream. That role makes Canary invaluable for catching subtle breakages early, but it also means individual flights can be unstable and may contain known blockers that should deter installation on production machines. Recent Canary builds in the 27xxx series have skewed toward reliability housekeeping rather than feature rollouts, and Build 27943 continues that pattern.

---

What Windows 11 Canary Build 27943 fixes​

Overview — the headline fixes​

• Storage → Temporary files scanning hang: The Settings UI could become stuck while scanning temporary files, and the “Clean up previous Windows installations” option sometimes failed to appear; this behavior is fixed in Build 27943.
• HDR toggle regression: HDR could immediately switch back to SDR right after being enabled; the build contains a fix so HDR remains enabled when requested from Settings.
• Taskbar duplicate preview thumbnails: A cosmetic but confusing issue where hovering a taskbar thumbnail could show duplicates after minimizing apps and switching virtual desktops has been addressed.
• Noisy Pluton Event Viewer errors: Spurious error entries tied to the Microsoft Pluton Cryptographic Provider (error ID noise) were generating needless alarms in Event Viewer; those log entries have been cleaned up for affected Insiders.

These fixes represent practical polish: they eliminate friction in routine workflows (disk cleanup and HDR management) and reduce false‑positive noise that can mislead end users and administrators.

Other targeted repairs​

• Restored Enter-as-confirm behavior when entering a PIN while casting from Quick Settings. This small I/O path fix smooths casting flows in meeting-room or presentation scenarios.
• Improved Group Policy Editor rendering for Chinese display language, removing blank layout areas that impeded administration tasks in that locale.

---

Deep dive: the Storage → Temporary files hang​

The symptom​

Some Insiders observed that when visiting Settings > System > Storage > Temporary files the scanner would hang while enumerating temporary content and previous Windows installations. The UI could appear frozen and — importantly — the option to “Clean up previous Windows installations” would not surface, preventing straightforward reclamation of multi‑gigabyte system backups. This was particularly painful for testers who frequently upgrade or roll back builds and rely on that UI for space management.

Why it mattered​

• Users with limited free disk space could not easily remove old Windows installation files after feature upgrades.
• Automated or scripted maintenance relying on UI‑exposed cleanup options was effectively blocked.
• The presence of a UI hang encouraged users to resort to more invasive measures (manual DISM/CleanupMgr commands or third‑party tools), increasing support burden.

The fix and practical impact​

The Canary flight fixes the enumeration path that was hanging the scan, allowing the Settings UI to complete its scan and correctly present the “clean up previous Windows installations” entry again. For Insiders who test upgrades frequently, this removes a recurrent friction point and restores a predictable cleanup flow.

---

Display and graphics: HDR and related quirks​

HDR toggling unexpectedly reverting​

A regression caused HDR to flip back to SDR moments after being switched on via Settings. That behavior broke color‑critical workflows for creators and gamers who expect immediate and persistent HDR activation. Build 27943 patches this toggling path so HDR remains active when users enable it in the Settings UI.

Additional graphics caveats to monitor​

Microsoft’s Canary notes and community reports also mention other graphics/audio edge cases that remain under investigation (browser-triggered flickers, PIX playback incompatibilities). Developers using DirectX tooling like PIX should be cautious — playback problems can interfere with GPU capture analysis workflows. The timeline for a PIX compatibility update is uncertain and should be treated as provisional until an official release is posted.

---

Taskbar, input, and localization fixes​

• The duplicate thumbnail preview issue after switching virtual desktops has been corrected, removing a disorienting visual duplication for heavy multitaskers.
• Quick Settings PIN-confirm: pressing Enter to confirm a casting PIN once again works, restoring a standard input expectation for that flow.
• Group Policy Editor layout for Chinese display language was improved to eliminate large blank areas, an important fix for administrators in affected locales.

These are small quality-of-life fixes, but they add up: the taskbar and input fixes reduce day‑to‑day friction, and the localization repair prevents administrative confusion in enterprise environments that use Chinese display locales.

---

Known issues and deployment risks — what Microsoft flagged​

Build 27943 is not without its caveats. Microsoft and community reporting highlight two high‑impact known issues that deserve explicit attention before installation:

• Installation rollback: Some devices experience rollbacks during installation with error codes in the 0xC1900101 family (examples reported: 0xC1900101‑0x20017 and 0xC1900101‑0x30017). Repeating the update frequently yields the same rollback. This is a true blocker for affected devices because the build will not stick.
• Arm64 kernel regression: Certain Arm64 devices have seen increased kernel bugchecks (IRQL_NOT_LESS_OR_EQUAL). On Arm64 hardware this can manifest as green‑screen crashes and unpredictable reboots, which risks data corruption and interrupts critical workloads. If you run Windows on Arm devices, treat this build as high risk.

Other issues still under investigation include graphics flicker scenarios and audio or PIX playback edge cases. Developers relying on GPU capture tooling should explicitly validate their toolchains before upgrading.

---

Release‑preview updates for Windows 11 and Windows 10 (KB5065790 and KB5066198)​

Alongside Canary activity, Microsoft pushed Release Preview channel updates:

• Windows 11 Build 22631.5982 — KB5065790: Delivered to Release Preview for Windows 11 version 23H2, this cumulative addresses several reliability items: a SIM PIN sign‑in freeze, Remote Desktop multi‑monitor crashes, printer queue UI crashes when viewing shared queues, and updates to mobile operator profiles (COSA). These fixes matter especially for remote/hybrid workers and WWAN/eSIM device fleets. (windowsreport.com)
• Windows 10 Build 19045.6388 — KB5066198: Released to Release Preview for Windows 10 version 22H2, this rollup focuses on general reliability improvements and performance tuning for devices remaining on Windows 10. Microsoft’s documentation for preview KBs can be sparse initially, so administrators should pilot these releases before broad deployment. (windowsreport.com)

These Release Preview updates are designed for organizations and users who need stability improvements without moving to a new feature update; they are not automatically equivalent to retail monthly cumulative updates, and formal Microsoft support articles may follow the initial flight notice.

---

Critical analysis — strengths, weaknesses, and practical implications​

Strengths​

• Targeted, user‑centric fixes: The Build 27943 changes focus on workflows that cause real friction — disk cleanup, HDR toggling, taskbar preview fidelity, and noisy security logs. Those are the kinds of small fixes that improve perceived stability quickly.
• Responsive Canary triage: Microsoft continues to use Canary as a fast feedback loop to eliminate regressions before they reach broader channels. The storage-scan and HDR fixes are examples of that responsiveness.
• Release Preview support for legacy fleets: KB5065790 and KB5066198 show Microsoft’s continuing commitment to smoothing real‑world reliability problems for Windows 11 and Windows 10 customers. (windowsreport.com)

Weaknesses and risks​

• Preview instability remains real: Canary is intentionally volatile. The rollback and Arm64 crash regressions are not cosmetic — they are deployment blockers and data‑integrity risks for affected devices.
• Sparse formal KB documentation for some preview updates: Administrators should be wary when official KB articles are delayed or minimal; limited documentation complicates change control and compliance validation.
• Tooling and developer friction: PIX playback and other DirectX/graphics tooling incompatibilities can hinder developer diagnostics and GPU capture workflows until compatible tooling updates ship. Treat any PIX-related timelines as unverified estimates until Microsoft or the PIX team publishes an official note.

---

Recommendations — who should install (and how)​

For production and managed endpoints​

• Do not install Canary builds on production machines or critical endpoints. The rollback and Arm64 kernel issues are real blockers.
• Validate Release Preview updates (KB5065790, KB5066198) in a controlled pilot group before broader rollout; prioritize devices experiencing the specific fixes (RDP multi‑monitor, SIM PIN sign‑in, printer queue crashes). (windowsreport.com)

For Insiders, developers, and power users (test rigs only)​

• Back up and image the device before upgrading. Create a full system image and confirm recovery media.
• If you use Arm64 hardware, avoid Build 27943 until Microsoft publishes a fix for the IRQL_NOT_LESS_OR_EQUAL regression.
• If you rely on PIX or other GPU capture tools, hold off or maintain a separate analysis machine until the tooling is validated against the Canary flight.

Installation checklist (short)​

• Confirm the device is in the correct Insider channel and that you intended to be in Canary.
• Create a full disk image and export system restore points.
• Ensure you have recovery media (bootable USB with Windows installation and latest drivers).
• Update firmware and third‑party drivers (graphics, storage, security agents) before installing.
• Pilot the build on a non‑critical machine for at least 48–72 hours, exercising workflows: RDP, multi‑monitor, HDR, printing, and any hardware‑specific workloads.

---

Troubleshooting and rollback mitigation​

If you encounter an installation rollback (0xC1900101 family codes):

• Record the exact error code and check Event Viewer and Setup logs (setuperr.log and setupact.log) to surface driver or firmware culprits.
• Boot into safe mode and uninstall recently installed drivers (graphics, storage, third‑party security).
• Use the previously created system image or Windows installation media to recover if the device does not boot.
• Report the issue to the Feedback Hub and attach relevant logs — early diagnostics help Microsoft identify driver- or OEM-related patterns.

If you experience Arm64 kernel bugchecks:

• Revert to the previous build and preserve memory dumps and minidumps for analysis.
• Avoid running long‑duration or write‑heavy workloads until a fix is available.

---

Final verdict​

Build 27943 is useful for Insiders who run dedicated test hardware: it restores a broken temporary file cleanup flow, fixes an annoying HDR toggle regression, and removes spurious Pluton event noise — all practical, user‑facing cleans. For the broader Windows audience, however, the Canary‑level known issues (installation rollbacks and an Arm64 kernel regression) make this flight inappropriate for daily‑driver and production machines. Administrators should focus on the Release Preview rollups (KB5065790 and KB5066198) as the safer path to evaluate reliability fixes for Windows 11 and Windows 10 respectively.
Microsoft’s cadence remains clear: Canary is the lab where regressions are fixed quickly but at the cost of volatility; Release Preview provides a safer channel for organizations that need fixes without feature churn. Use the right channel for your risk profile, back up before you test, and treat Canary flights as alerting signals rather than ready‑for‑prime‑time fixes.

---

Appendix — quick reference (one‑page)

• Build: Windows 11 Insider Preview Build 27943 (Canary) — fixes: Temporary files scan hang; HDR toggling; taskbar thumbnail duplication; Pluton Event Viewer noise; Quick Settings PIN confirmation; Group Policy Editor (Chinese).
• Known blockers: 0xC1900101 rollback errors; Arm64 IRQL_NOT_LESS_OR_EQUAL bugchecks; PIX playback/graphics edge cases.
• Related Release Preview updates: KB5065790 (Windows 11, 23H2) and KB5066198 (Windows 10, 22H2) — pilot these on representative devices before wide deployment. (windowsreport.com)

This build is a reminder that small, user‑facing regressions can have outsized annoyance and operational cost — and that the fastest way to stop them is to test early, iterate quickly, and roll fixes through the right release channels.

---

Source: Windows Report Windows 11 Canary Preview Build 27943 fixes stuck temporary file cleanup and HDR issues