[BUG] Claude Desktop (Windows, MSIX) fails every launch after update to 2.16120.0.0 — "untrusted mount point" (0x800701C0), clean reinstall does not help

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

This is a Claude Desktop (Windows, MSIX) bug, not the CLI. Filing here because this repo is where desktop issues are triaged.

Since the update from 2.9939.4.0 to 2.16120.0.0, Claude Desktop fails on every launch with the Windows dialog:

The path cannot be traversed because it contains an untrusted mount point.

referencing C:\Program Files\WindowsApps\Claude_2.16120.0.0_x64__pzs8sxrjxfjjc\app\Claude.exe.

Claude never gets as far as its own startup: main.log is not written, and no Claude data folder is created in the package's LocalCache\Roaming. The failure happens while Windows creates the Desktop AppX container:

• AppModel-Runtime 216: 0x800701C0: Cannot create the Desktop AppX container for package Claude_2.16120.0.0_x64__pzs8sxrjxfjjc because an error was encountered configuring the runtime.
• AppModel-Runtime 208: 0x800701C0: Cannot create the process for package Claude_2.16120.0.0_x64__pzs8sxrjxfjjc because an error was encountered while configuring runtime. [LaunchProcess]

0x800701C0 = ERROR_UNTRUSTED_MOUNT_POINT (Win32 448).

The same machine and configuration launched 2.9939.4.0 without problems the day before. The last Windows update was two weeks earlier.

What Should Happen?

Claude Desktop 2.16120.0.0 launches normally, as 2.9939.4.0 did on the same machine and configuration.

Error Messages/Logs

Dialog:
The path cannot be traversed because it contains an untrusted mount point.
C:\Program Files\WindowsApps\Claude_2.16120.0.0_x64__pzs8sxrjxfjjc\app\Claude.exe

Microsoft-Windows-AppModel-Runtime/Admin (every launch attempt):
Id 216  0x800701C0: Cannot create the Desktop AppX container for package Claude_2.16120.0.0_x64__pzs8sxrjxfjjc because an error was encountered configuring the runtime.
Id 208  0x800701C0: Cannot create the process for package Claude_2.16120.0.0_x64__pzs8sxrjxfjjc because an error was encountered while configuring runtime. [LaunchProcess]

Last successful launch (AppModel-Runtime Id 201):
2026-09-29 11:54  Created process … in package Claude_2.9939.4.0_x64__pzs8sxrjxfjjc. [LaunchProcess]

Microsoft-Windows-AppXDeploymentServer/Operational, during a first reinstall attempt while a Claude process was still running:
Id 8107  Illegal non-AppStore or non-AppInstaller package integrity validation attempted for package Claude_2.16120.0.0_x64__pzs8sxrjxfjjc. Flags: 0x0
Id 8104  Failed to set the Trust Label on package Claude_2.16120.0.0_x64__pzs8sxrjxfjjc with flags 0x0. Error: 0x80070057.
Id 419/404/401  0x80073D02: Unable to install because the following apps need to be closed Claude_2.16120.0.0_x64__pzs8sxrjxfjjc.

Clean reinstall after removal and reboot (all succeeded, launch still fails identically):
Remove   Claude_2.16120.0.0_x64__pzs8sxrjxfjjc  finished successfully
Add      Claude_2.16120.0.0_x64__pzs8sxrjxfjjc  finished successfully
Register Claude_2.16120.0.0_x64__pzs8sxrjxfjjc  finished successfully

Steps to Reproduce

1. Have Claude Desktop 2.9939.4.0 (MSIX) installed and working.
2. The app updates to 2.16120.0.0.
3. Launch Claude from the Start menu. The "untrusted mount point" dialog appears, and AppModel-Runtime logs 216 and 208 with 0x800701C0.
4. Stop CoworkVMService and all Claude processes, then run Get-AppxPackage *Claude* -AllUsers | Remove-AppxPackage -AllUsers, reboot, and reinstall from claude.ai/download. The same failure occurs on every launch.

Diagnostics performed (all negative):

• No junctions or symlinks (LinkType empty) on %USERPROFILE% and its direct subfolders, %APPDATA%, %LOCALAPPDATA% and their direct subfolders, AppData\LocalLow, %TEMP%, %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc (recursive, depth 3), C:\ProgramData, C:\Program Files, C:\Program Files (x86), Common Files, C:\Users\Public, C:\Users\Default
• The package is installed in the default location (C:\Program Files\WindowsApps\…), not moved to another volume
• Other packaged apps launch fine, including packaged desktop apps (Calculator, Windows Terminal, Paint), so the WindowsApps ACL and the container infrastructure work in general
• The Windows optional feature Containers is disabled
• No Dev Drive, and all volumes are NTFS (fsutil devdrv query reports "This is not a developer volume")
• No Claude or Cowork processes running before the launch attempt, and CoworkVMService stopped
• No leftover %APPDATA%\Claude or %LOCALAPPDATA%\AnthropicClaude

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Claude Desktop MSIX 2.9939.4.0

Claude Code Version

N/A — Claude Desktop MSIX 2.16120.0.0 (not the CLI)

Platform

Other

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Environment

• Windows 11, build 26200.9457, x64
• Last Windows updates: KB5129195 (2026-09-15), KB5124007 (2026-09-09), KB5126052 (2026-09-08). All of them predate the last successful launch on 2.9939.4.0.
• Claude Desktop MSIX, SignatureKind from the claude.ai/download installer, package family Claude_pzs8sxrjxfjjc

This configuration worked with 2.9939.4.0 and earlier.

Related issues

• #68070: same error text and NTSTATUS family (STATUS_REDIRECTION_NOT_TRUSTED). There the suspected factor was a Dev Drive, which does not apply here.
• #37068: same HRESULT 0x800701C0, but in the Cowork HCS Construct phase with the Windows Containers feature enabled. Here the app container itself fails and Containers is disabled.
• #53247: same event IDs 208/215 after updates, but with 0x80070020 and recoverable by logoff or reboot. Here a reboot does not help.

Happy to run further diagnostics, provide full event log exports, or test a build.