Microsoft 365 Add-ins Not Working

Since restart, sign-out/sign-in, Office update, and PC restart were already tried, the next useful checks are these:

1. Check whether this is a current Microsoft 365 add-in service issue.
   • There are known issues where centrally deployed or organization-managed Office add-ins may disappear, fail to load, or appear unavailable across Excel desktop, Excel on the web, and other Office clients.
   • There is also a known issue where some add-ins failed to update through the Store and then would not load.
   • In those cases, waiting and retrying can help while mitigations roll out.
2. Refresh admin-managed add-ins.
   • In the Office app, select Home > Add-ins.
   • Select More add-ins.
   • Open the Admin Managed tab.
   • Select Refresh.
   • Then try opening the add-in again.
3. If the add-in was installed from the Store and is failing after an update attempt:
   • Close and reopen the Office app.
   • Retry the add-in update or reload after some time.
4. If an ADD-IN INFORMATION message appears in the task pane:
   • This usually indicates a Microsoft 365 tenant configuration issue rather than a problem with the add-in itself.
   • In that case, the Microsoft 365 administrator needs to review the tenant add-in settings.
5. If the problem happens during installation and shows "Error loading add-ins":
   • Close Office.
   • Check that the computer date and time are correct.
   • Verify the add-in manifest is valid.
   • Restart the add-in.
   • Install the add-in again.
   • If the package was tampered with before installation, download it again or contact the add-in publisher.
6. Test whether another add-in is interfering with Office startup.
   • Start the Office app in Safe Mode:
     • excel /safe for Excel
     • winword /safe for Word
     • powerpnt /safe for PowerPoint
   • If the app works in Safe Mode, go to File > Options > Add-Ins.
   • In Manage, choose the app add-ins type or COM Add-ins, then select Go.
   • Disable add-ins one at a time and test again.
7. If the add-ins are organization-deployed:
   • Verify the user has access to required Microsoft 365 and Exchange Online services.
   • If the organization restricts Exchange Web Services (EWS), verify required access settings are enabled.
   • There is a known issue tied to Exchange authentication changes that caused some admin-deployed add-ins to appear missing or fail to deploy.
8. If the issue still persists:
   • Collect diagnostic information such as session IDs, correlation IDs, logs, or network traces if available.
   • Contact Microsoft Support.
   • If this is a work or school account, the Microsoft 365 admin should open the support case.

If the exact symptom is available, the next step can be narrowed down further:

• add-in missing from ribbon
• add-in visible but not loading
• add-in install fails
• only Outlook affected
• only centrally deployed/admin-managed add-ins affected
• specific error text such as "You don't have permission to use this add-in" or "Error loading add-ins"

References:

• Office Add-ins known issues
• Troubleshoot user errors with Office Add-ins
• I get a "stopped working" error when I start Office applications on my PC