Microsoft To-Do sync broken — Graph API returns 500 Internal Server Error on /me/todo/lists

Account: my personal microsoft account

Issue: Microsoft To-Do has stopped syncing on all clients (web, Android app, Windows app) since approximately 2026-08-17 ~10:00 UTC. All clients show "syncing" indefinitely and never load any lists or tasks.

What I've tested:

• To-Do Web UI (to-do.microsoft.com) — loads the shell but gets stuck infinitely. Browser DevTools show a 500 error on:The app cannot finish bootstrapping because of this failing endpoint.
  • PATCH https://substrate.office.com/todob2/api/v1/settings/WunderlistImportStatus → 500
• To-Do Android app — stuck on "syncing", never loads any lists.
• Microsoft Graph Explorer — GET https://graph.microsoft.com/v1.0/me/todo/lists returns:
  • { "error": { "code": "UnknownError", "message": "", "innerError": { "date": "2026-08-17T14:49:16", "request-id": "1a8ecd9b-ad9d-4801-9f17-93d243ab6d7a", "client-request-id": "89c63f17-7b32-2cc8-df82-0712bd11e59f" } } }
• Other Microsoft 365 services — OneDrive works fine, test file synced. Account authentication is valid (Graph Explorer successfully queries /me).
• Re-login, account removal/re-add — tried on all clients, no change.
• No third-party integrations modified task data — verified via local opencode session database (zero Microsoft Graph/To-Do API calls found in any session). Never used any other 3rd party integration.

Conclusion: The issue is a server-side error in the To-Do backend. The Graph API itself (/me/todo/lists) returns 500, and the substrate settings API also returns 500. This is not a client-side issue, not an authentication issue, and not caused by any third-party integration. The account-specific error suggests corrupted backend state or a service-side bug affecting this specific account.

Request: Please investigate the server-side error for my account usinng the provided request IDs and restore To-Do sync access.