[BUG] Claude Desktop (Windows, MSIX): sessions vanished from about a dozen projects at once; project folder reported as "on another computer"

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?

On 2026-10-01, around 2:20 PM Pacific, sessions disappeared from the sidebar across about a dozen of my projects at once. Most of my pinned projects are now missing all of their sessions or the majority of them. I did not delete, rename, or archive anything.

The two cases below are the ones I could verify in detail. They are examples, not the full scope.

Example project: Core30

1. A session named "Core30". Active that morning. A summary snapshot I saved from it at 11:21 AM exists on disk, so the session definitely existed.
2. A microsites session with several hours of work. It was writing files into the project folder until at least 12:14 PM.

The project now shows only a new session I opened after noticing the loss.

Symptom at the same time: the project's linked folder (D:\Dropbox\Core30) now shows "To use these files anywhere, upload them from the computer that has this folder." The folder is present on this machine. It syncs via Dropbox to a second Windows machine where I also use these projects.

What I checked

• Local session storage (LocalCache\Roaming\Claude\local-agent-mode-sessions under the MSIX package) has nothing newer than 2026-08-11, so these were cloud sessions.
• Account data export (90 days): neither Core30 session is present. A different session also named "Core30", still visible in the sidebar under another project, is also absent from the export, so the export does not contain all sessions.
• In-app chat search scoped to the project returns nothing.
• All files the sessions wrote are intact on disk. Only the conversations are gone.

Possibly related:

• #80061 session header shows cloud project while "Change project" shows local project of the same name
• #79829 Windows: project Recents list sessions from OTHER projects (post-unification)
• #79422 Desktop Windows: global session list frozen at a past cutoff while project list differs
• #69663 Cowork sessions missing from Recents on Windows
• #57227 sessions not visible in sidebar, need indexing recovery
• #45076 Cowork session history silently lost

What Should Happen?

Sessions persist in their project, or remain findable through search and the data export, regardless of the project folder's link state or which synced machine opened it last.

Error Messages/Logs

No error was shown. The sessions silently dropped out of the sidebar.

Project page message at the same time:
"To use these files anywhere, upload them from the computer that has this folder."

Steps to Reproduce

Not reliably reproducible on demand. Conditions when it occurred:

1. Many Cowork projects, each with a linked local folder inside Dropbox (e.g. D:\Dropbox\Core30), used from two Windows machines that both sync those folders.
2. Sessions created and worked in across those projects over recent days, several on the day of the loss.
3. Around 2:20 PM Pacific on 2026-10-01, sessions disappeared from roughly a dozen projects at once. At least one project began reporting its folder as being on another computer at the same time.
4. Missing sessions are not found by project search, local session storage, or the account data export.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude Desktop 2.16120.0 (Windows, Microsoft Store / MSIX build)

Platform

Other

Operating System

Windows

Terminal/Shell

Other

Additional Information

Scope: this hit roughly a dozen projects simultaneously, not one. It looks account-wide or tied to the session-to-project mapping, not a single project's folder.

Impact: hours of reasoning and decisions per session, across many client projects, that cannot be reconstructed from the output files. A support ticket is open. I have not removed or re-linked any project folder, reinstalled, or signed out, to avoid destroying anything recoverable.

If these sessions are recoverable server-side, please advise how.