We are experiencing a reproducible issue across multiple Windows 11 devices that appears to be related to a recent cumulative update and user-session runtime state, not a specific application.

Summary

We are experiencing a reproducible issue across multiple Windows 11 devices that appears to be related to a recent cumulative update and user-session runtime state, rather than any specific application.

After installing the April 2026 Windows 11 cumulative update, some users experience application crashes tied to new event processing (e.g., new email arrival) on a consistent ~24-hour cadence per user.

Key Symptoms

• Outlook Classic (Win32) crashes when a new email is received
• Outlook New (WebView-based) also crashes under the same conditions for some users
• In some cases, Windows Explorer becomes unresponsive after the crash
• Prior to the first crash:
  • Outlook stops delivering Windows desktop notifications
• After the issue occurs once:
  • Outlook crashes on every newly received email
• Restarting Outlook:
  • Loads existing mail
  • Crashes on the next new email

Recovery Behavior

• Resolved immediately by signing out of Windows and signing back in
• Also resolved by full system reboot
• Not resolved by restarting Outlook or related processes/services

This strongly indicates the issue is tied to per-user Windows session state, rather than application-level state.

Timing / Pattern

• Occurs approximately every 24 hours, often down to the minute, per affected user
• After the user signs out and signs back in:
  • The issue returns again ~24 hours later
• The exact time differs per user, but is consistent for each individual

Scope / Environment

• Impacts multiple users (not all devices)
• Reproduces on:
  • Existing machines
  • Newly provisioned machines
• Systems are:
  • Fully up to date (Windows, Office, and Edge components)
  • Entra joined
  • Using modern authentication and standard Microsoft 365 configurations

Troubleshooting Performed

The following actions have not resolved the issue:

• Repairing or reinstalling Office
• Recreating Outlook profiles
• Running Outlook in Safe Mode
• Disabling all add-ins
• Testing on newly provisioned/clean systems
• Running sfc /scannow and DISM repairs

Additional Observations

• Issue occurs in both Classic and New Outlook, which use different architectures
• Cannot be reproduced through admin impersonation
• Appears to be tied to a time-based or lifecycle-based trigger
• Once triggered, persists until the user session is reset (logoff)

Current Mitigation

Users must sign out of Windows and sign back in (approximately once every 24 hours) to restore functionality.

Question

Has anyone else observed similar behavior after the April 2026 Windows 11 cumulative update?

Specifically:

• Application crashes tied to event triggers (e.g., new email)
• Occurring on a fixed interval (~24 hours)
• Resolved only by user logoff/logon or reboot

Any confirmation of a known issue or guidance would be appreciated.

Reference

Original thread with earlier troubleshooting context:

After Installing 2024-04 Windows Update, Both New and Old Outlook Unusable

Reddit Post about this same issue:

Outlook (Classic) issues after 2026-04 Windows Update