Which problem does this cover?
Checked: 7 September 2026. This researched guide covers classic Outlook for Microsoft 365: opening Copilot leaves the chat area showing three dots. It is not a general fix for missing licences, sign-in problems or new Outlook. We have not reproduced the issue on our own device.
Install the corrected version first
Microsoft lists the fix in Current Channel 2607, build 20228.20190, and Monthly Enterprise Channel 2607, build 20228.20188. Match the build to your update channel.
- Open File → Office Account and record the version, build and update channel.
- Use Update Options → Update Now to install the correction offered for your channel or a newer version. If updates are centrally managed, give these details to IT; do not change the channel yourself.
- Save your work, restart Outlook and open Copilot again. If the interface loads, no cache intervention is needed.
Cache workaround with a backup
For a matching case that persists, Microsoft documents rebuilding the web add-in cache:
- Save your work and close Outlook and all other Office applications.
- In File Explorer, open
%LOCALAPPDATA%\Microsoft\Office\16.0. - Rename only
Weftowef.old. If the folder is missing or the backup name already exists, do not guess or overwrite it; ask IT to check. - Start Outlook. It recreates the cache. Check Copilot and the web add-ins you use.
Verify, undo and escalate
Success means the Copilot interface loads fully and still works after another Outlook restart. To undo the change, close Office, keep the newly created Wef folder under an unused backup name, then rename wef.old back to Wef. This may restore the original problem.
Do not delete PST/OST files or mail profiles. If the problem continues, give support the build, channel and steps observed, without confidential email content. Rebuilding the cache does not replace a suitable licence or diagnosis of another fault.