Microsoft’s August cumulative for Windows 11 (KB5063878, OS Build 26100.4946) shipped with security fixes — and within days the patch was linked to two very different reliability problems: an enterprise deployment failure that produced WSUS/SCCM install errors, and a separate cluster of community‑reproduced reports showing storage devices vanishing during sustained large writes, with an attendant risk of file corruption and data loss.
Microsoft released KB5063878 for Windows 11 version 24H2 on August 12, 2025 as part of its regular Patch Tuesday rollup. The update is listed as OS Build 26100.4946 and bundles security fixes and servicing-stack improvements. Microsoft’s official release notes for the package did not initially list a storage regression as a known issue.
Only weeks earlier Microsoft had publicly declared Windows 11 24H2 “the most reliable version of Windows yet,” citing telemetry that showed a 24% drop in unexpected restarts versus Windows 10 22H2 — a claim that framed KB5063878 as a routine security/quality rollout rather than anything experimental. The contrast between that messaging and the problems that followed is striking.
Within 48–72 hours of the roll‑out multiple independent community testers and enthusiast outlets began reporting a reproducible pattern: during sustained, large sequential write operations (commonly around ~50 GB or more), certain SSDs and a small number of HDDs could stop responding, disappear from the OS topology, and return unreadable SMART/controller data; files written in the affected window sometimes appeared corrupted or were missing after a reboot. Reports singled out drives using Phison controller families as disproportionately represented among affected samples, although the phenomenon was not strictly limited to Phison‑based SSDs. (igorslab.de, guru3d.com)
Caveat: these are plausible explanations inferred from community reproductions and the failure fingerprint. Definitive attribution requires vendor and Microsoft telemetry and is not yet public.
Practical actions: back up now, avoid bulk writes on systems that have installed the update, pause deployments in enterprise environments, coordinate with SSD vendors for firmware guidance, and watch Microsoft’s Windows release health and vendor advisories for a confirmed fix. Treat public reports of permanent drive bricking as unverified until vendors provide forensic confirmation. (windowsforum.com, bleepingcomputer.com)
The pattern here is familiar: updates fix some problems and, occasionally, reveal new edge cases in a complex hardware ecosystem. The difference this time is the immediate risk to user data during large‑file operations; that elevates this from a convenience bug to a potentially destructive regression. Prioritize backups, staged deployments, and vendor coordination until vendors and Microsoft publish confirmed remediation. (notebookcheck.net, guru3d.com)
Source: PC Guide Latest Windows 11 update could damage your data, less than a month since Microsoft called it the most reliable
Overview
Microsoft released KB5063878 for Windows 11 version 24H2 on August 12, 2025 as part of its regular Patch Tuesday rollup. The update is listed as OS Build 26100.4946 and bundles security fixes and servicing-stack improvements. Microsoft’s official release notes for the package did not initially list a storage regression as a known issue. Only weeks earlier Microsoft had publicly declared Windows 11 24H2 “the most reliable version of Windows yet,” citing telemetry that showed a 24% drop in unexpected restarts versus Windows 10 22H2 — a claim that framed KB5063878 as a routine security/quality rollout rather than anything experimental. The contrast between that messaging and the problems that followed is striking.
Within 48–72 hours of the roll‑out multiple independent community testers and enthusiast outlets began reporting a reproducible pattern: during sustained, large sequential write operations (commonly around ~50 GB or more), certain SSDs and a small number of HDDs could stop responding, disappear from the OS topology, and return unreadable SMART/controller data; files written in the affected window sometimes appeared corrupted or were missing after a reboot. Reports singled out drives using Phison controller families as disproportionately represented among affected samples, although the phenomenon was not strictly limited to Phison‑based SSDs. (igorslab.de, guru3d.com)
Background: what shipped and how the problems unfolded
The update and its stated scope
KB5063878 was released as a standard August cumulative update for Windows 11 24H2. Officially it bundled security updates and quality fixes and updated several AI and servicing components; the public KB article contains build and component details and standard installation guidance. Microsoft’s KB page initially listed no storage‑device faults.Two separate failure modes emerged quickly
- Enterprise deployment errors (0x80240069) — Administrators deploying KB5063878 via WSUS and System Center Configuration Manager (SCCM) reported repeated install failures where the Windows Update Agent service stopped and the error code 0x80240069 appeared in logs. Microsoft acknowledged this WSUS/SCCM delivery issue and rolled out a Known Issue Rollback (KIR) mitigation for enterprise environments while a permanent servicing fix was prepared.
- Storage regression during heavy writes — Independent testers reproduced a storage regression where drives could become unresponsive and disappear mid‑transfer during large sequential writes (around ~50 GB+). Symptoms include frozen copy operations, the target drive vanishing from File Explorer, Device Manager and Disk Management, unreadable SMART/controller telemetry, and cases of file or metadata corruption after a reboot. Community collations and hands‑on testing singled out a number of Phison‑controller‑based SSDs among the affected devices, but other controllers and some HDDs surfaced in reproductions as well. (notebookcheck.net, windowsforum.com)
Symptoms, trigger profile, and affected hardware
Typical symptoms reported by testers and end users
- Sustained large file copies or continuous writes (often cited ~50 GB or more) begin normally and then abruptly fail or stall.
- The storage device disappears from Windows: it no longer appears in File Explorer, Device Manager, Disk Management, or SMART utilities.
- Rebooting the PC sometimes restores the device’s visibility but does not guarantee the integrity of files written during the failure window.
- In a minority of reports the drive remained inaccessible after reboot and required reformat or vendor recovery steps. (windowsforum.com, igorslab.de)
Workload that appears to trigger the issue
Community tests converged on a sustained sequential write pattern as the most reliable trigger — heavy, continuous writes that exercise the drive’s controller cache and metadata paths for multiple seconds or minutes (typical reproduction windows were in the ~50 GB+ range). This workload profile is common for game updates, large media copies, disk clones, and video production exports.Which drives are more likely to show the fault
- Early reproductions flagged Phison‑controller families (examples: PS5012‑E12, E21T, E31T families) as more frequently implicated, especially on DRAM‑less or HMB‑reliant designs.
- However, testers and aggregated lists also include branded models from several vendors (Corsair, Kioxia, SanDisk, Crucial, WD, and others), showing the issue is not strictly tied to a single brand.
- A handful of enterprise HDDs showed similar disappearances under intense sequential writes in some reproductions, suggesting the regression may be in the host/OS I/O stack rather than purely a single controller firmware bug. (igorslab.de, guru3d.com)
Technical analysis: plausible causes and what the evidence suggests
Diagnosing storage regressions requires careful separation of symptoms and root cause. The evidence shared publicly so far supports a few plausible explanations — none yet definitively confirmed by Microsoft or SSD vendors.1) OS‑level regression in buffered I/O or NVMe handling
A small change at the kernel or NVMe driver level — for example, altered timing, command ordering, or buffer management — can expose latent bugs in controller firmware. If the host issues a sequence that the firmware mishandles under heavy sequential load, the controller may lock up or cease replying to admin commands, making the SSD appear "removed" from the PCIe or storage topology. Several community posts characterized the behavior as consistent with a controller lock‑up triggered by an OS change. (windowsforum.com, igorslab.de)2) Host Memory Buffer (HMB) and DRAM‑less SSD interactions
Past incidents during the 24H2 rollout were rooted in how Windows allocated HMB for DRAM‑less drives: increased host HMB allocations pushed some controllers into unstable regions. While the current reports don’t uniformly point to HMB, the pattern of heavy sequential writes stressing a controller’s caching and mapping paths echoes earlier HMB‑related regressions that required firmware and OS adjustments.3) Controller firmware edge cases under sustained high utilization
Controller firmware maintains metadata and wear‑leveling tables during writes; an unexpected host behavior or timing could trigger an internal condition that causes the controller to stop responding. Community reproductions showing unreadable SMART and controller telemetry after the failure are consistent with a controller or firmware hang. Several affected models share similar firmware families (Phison-based controllers), which supports the firmware‑sensitivity hypothesis — but the presence of non‑Phison examples means the OS stack remains a strong suspect. (igorslab.de, guru3d.com)Caveat: these are plausible explanations inferred from community reproductions and the failure fingerprint. Definitive attribution requires vendor and Microsoft telemetry and is not yet public.
What Microsoft has said (and not said)
- Microsoft published the KB page for KB5063878 (OS Build 26100.4946) with the update’s official scope and did not list a storage disappearance issue as a known problem at publication.
- Microsoft did acknowledge and mitigate the WSUS/SCCM install failure (error 0x80240069) with a Known Issue Rollback for enterprise-managed devices; guidance and KIR deployment were provided to administrators. That enterprise installation issue is separate from the storage disappearance reports.
Practical risk assessment: how severe is this?
- Data integrity risk — high: when a drive disappears mid‑write there is a real risk of incomplete metadata updates and file corruption. Several community reports include corrupted or missing files after the device was restored, which raises the risk profile above a transient crash. (notebookcheck.net, windowsforum.com)
- Scope — currently limited but non‑negligible: the issue, as reported, is not universal across all devices and appears tied to specific controller/firmware/host combinations and a specific workload. That said, the workload (50 GB+ writes) is commonplace for gamers, video professionals, and anyone installing large packages.
- Enterprise impact — compounded: enterprises face not only the deployment error (0x80240069) but also the potential for data loss on workstations that handle large file transfers. This creates a dual operational risk: delayed patching or exposure if admins block the update, and data integrity hazards if it’s deployed unchecked. (bleepingcomputer.com, windowsforum.com)
Clear, practical guidance for users and admins
The priority is to avoid data loss and to give vendors and Microsoft time to investigate. The following steps are ordered by priority and practicality.Immediate actions for all users
- Back up critical data now. Copy essential files to a secondary, unaffected drive or cloud storage before performing any large write tasks or installing the KB. Backups are the only guaranteed way to avoid irreversible loss.
- Avoid sustained large writes (≥~50 GB) on at‑risk systems. Postpone big game installs, disk clones, video exports, or bulk file copies until the situation is clarified. Splitting transfers into smaller batches reduces the chance of triggering the workload pattern.
- Monitor your system during writes. If you see significant slowdowns, stalled copies, or the target drive disappears, stop, eject (if possible), and back up what you can to an unaffected target. Reboots sometimes restore visibility but do not guarantee file integrity.
If you already installed KB5063878
- Temporarily avoid heavy write operations. If you must do so, use an alternate drive that is known unaffected (for example, a drive with different controller family or an external backup drive).
How to roll back or remove KB5063878 (enterprise & consumer options)
- Consumer rollback (Settings):
- Settings > Windows Update > Update history > Uninstall updates — select the August cumulative and uninstall. This removes the LCU if the OS allows it. Some combined packages that include SSU content may not be fully removable by Settings alone.
- Advanced removal (DISM):
- For administrators or advanced users, Microsoft documents using DISM to list installed packages and remove the LCU by package name:
DISM /Online /Get-PackagesthenDISM /Online /Remove-Package /PackageName:<name>. Use caution: removing servicing stack updates or partial SSU content can leave the system in an inconsistent servicing state if not done correctly. - Enterprise mitigation (WSUS/SCCM):
- If you manage updates via WSUS/SCCM and experienced 0x80240069, deploy the Known Issue Rollback Group Policy guidance Microsoft issued and resync clients as recommended; the KIR mitigated the enterprise delivery fault while Microsoft prepared a servicing fix.
For administrators and IT teams
- Pause automated deployment of KB5063878 to production rings until vendor confirmation or Microsoft advisories are available. Deploy to a limited pilot ring and run scripted large‑write tests on a matrix of hardware/firmware to validate.
- Coordinate with SSD vendors: open support tickets with affected hardware vendors and request firmware diagnostic instructions and telemetry capture steps. Vendors may release firmware updates or guidance specific to controller revisions.
- Document and collect evidence: if you encounter the issue gather system logs, copy operation traces, SMART dumps, and, if possible, vendor logs. These artifacts are essential for vendor/Microsoft triage.
What vendors and Microsoft should do (and what to watch for)
- SSD vendors should triage customer reports, validate reproductions across firmware revisions, and publish explicit firmware advisories or updates where appropriate. Community reproductions have already produced candidate model lists; vendors need to confirm or deny those lists with telemetry and firmware forensics. (igorslab.de, guru3d.com)
- Microsoft should reproduce the failure on in‑house test matrices, publish a Windows release‑health advisory if confirmed, and deploy a targeted KIR or servicing patch to remove the regression. Until Microsoft posts a storage‑specific advisory, the community‑sourced evidence is credible but not definitive. (support.microsoft.com, windowsforum.com)
Strengths and weaknesses of the ecosystem response
Strengths
- Rapid community triage and sharing has surfaced reproducible test vectors fast; hands‑on testing by enthusiasts and publications provides early, actionable indicators that accelerate vendor triage. (notebookcheck.net, guru3d.com)
- Microsoft’s Known Issue Rollback mechanism and quick mitigation for the WSUS/SCCM install failure demonstrate the platform’s ability to respond to delivery regressions in enterprise contexts.
Weaknesses and risks
- Broad hardware diversity makes pre‑release testing for every firmware/version combination impractical; rare edge cases can still slip through to broad rollouts. This incident underscores the fragility of interactions between the OS I/O stack and diverse controller firmware.
- Data‑integrity outcomes are severe. A vanished drive during writes is more than an annoyance; it can destroy user trust and cause irreversible loss for users without reliable backups. Community reports of corrupted partitions or unrecoverable volumes — while not yet comprehensively verified — make this particularly worrying.
Conclusion — short, practical summary
The August cumulative KB5063878 (OS Build 26100.4946) for Windows 11 24H2 was released as a security/quality rollup. Within days, community testing connected the package to two distinct reliability incidents: a WSUS/SCCM deployment failure (0x80240069) that Microsoft mitigated via Known Issue Rollback, and an emergent storage regression where some SSDs/HDDs can disappear under sustained large writes — with possible file corruption. The storage regression has been reproduced by multiple independent testers and covered by several tech outlets, but official vendor/Microsoft confirmation of the storage issue and a definitive root‑cause remains pending. (support.microsoft.com, bleepingcomputer.com, igorslab.de)Practical actions: back up now, avoid bulk writes on systems that have installed the update, pause deployments in enterprise environments, coordinate with SSD vendors for firmware guidance, and watch Microsoft’s Windows release health and vendor advisories for a confirmed fix. Treat public reports of permanent drive bricking as unverified until vendors provide forensic confirmation. (windowsforum.com, bleepingcomputer.com)
The pattern here is familiar: updates fix some problems and, occasionally, reveal new edge cases in a complex hardware ecosystem. The difference this time is the immediate risk to user data during large‑file operations; that elevates this from a convenience bug to a potentially destructive regression. Prioritize backups, staged deployments, and vendor coordination until vendors and Microsoft publish confirmed remediation. (notebookcheck.net, guru3d.com)
Source: PC Guide Latest Windows 11 update could damage your data, less than a month since Microsoft called it the most reliable
