Outlook for Mac add-in fails with “We couldn't access 'Add-in Name'” until cache clear – Issue affecting some users for 3 days, requesting RCA and guidance

Hello Seclore,

It has been a while and I am writing to see how things are going with this issue. Have you had a chance to check the replies provided? Any update would be appreciated.

If the answer is helpful, please mark it as an answer, which will definitely help others in the community who have similar queries to find solutions to their problems faster. Thank you for your understanding.  

Best Regards, 

Demi-N | Microsoft Community Support Specialist

Hello Seclore,

Welcome to Microsoft Support and thank you for providing a comprehensive overview of the issue affecting your Office Web Add-in on Outlook for Mac.

Based on our investigation and current telemetry, here are our findings and recommendations:

This issue appears to be related to a corruption or inconsistency in the Office Web Add-in cache on Outlook for Mac. Specifically:

• The Wef (Web Extension Framework) and WebKit caches store resources for Office Add-ins. When these caches become stale or corrupted, the add-in may fail to load properly.
• The fact that OWA works fine for the same users confirms the issue is isolated to the local Outlook for Mac client environment.
• There have been no recent changes to your add-in, but Microsoft did release updates to Outlook for Mac in recent builds that may have introduced stricter cache validation or changes in how WebView2 handles cached content. You can refer to the full update history here: Update history for Microsoft 365 Apps (listed by date)

Based on the above analysis, we recommend the following next steps and mitigation strategy to address the issue and reduce the likelihood of recurrence:

1. Scalable Cache Clearing

We acknowledge that your team has already applied manual cache clearing steps successfully. To scale this solution across affected users, we recommend automating the same process via your organization’s MDM platform (e.g., Intune or Jamf). This would allow you to deploy the cache removal script programmatically, avoiding manual intervention on individual devices.

Please ensure the script is tested in a controlled environment before broad deployment:

rm -rf ~/Library/Containers/com.microsoft.Outlook
rm -rf ~/Library/WebKit/com.microsoft.Outlook
rm -rf ~/Library/Containers/com.microsoft.Outlook/Data/Library/Application\ Support/Microsoft\ Outlook

For reference, Microsoft provides guidance on clearing Office Add-in cache across platforms here: Clear the Office cache – Office Add-ins

2. Preventive Measures

• Ensure all users are on the latest stable build of Outlook for Mac.
• Avoid sideloading or modifying manifests directly on production environments, as this can lead to cache mismatches.
• Monitor for any add-in disablement due to performance thresholds (CPU/memory) as Outlook may automatically disable add-ins under certain conditions.

You may also find this troubleshooting guide useful for identifying and resolving common add-in issues: Troubleshoot user errors with Office Add-ins

If you wish to escalate this issue for deeper analysis or request a formal Root Cause Analysis (RCA), we recommend submitting a support request through one of the following channels:

• Microsoft 365 Admin Center: Admins can go to https://admin.microsoft.com, navigate to Support > New service request, and submit a ticket with relevant logs and details. This will route the case to the appropriate engineering team.
• Microsoft Premier or Unified Support: If your organization has a support agreement, you may contact your Technical Account Manager (TAM) or use the dedicated support portal for prioritized handling and RCA documentation.

To proceed with a formal RCA, we recommend collecting the following from an affected user:

• Outlook logs (via Help > Contact Support > Include Logs)
• Console logs during add-in load failure
• Fiddler trace (if applicable)

Additionally, Microsoft maintains a list of known issues and workarounds for Outlook for Mac, which may help identify related behaviors: Fixes or workarounds for recent issues in Outlook for Mac

To proceed with a formal RCA, we recommend collecting the following from an affected user:

• Outlook logs (via Help > Contact Support > Include Logs)
• Console logs during add-in load failure
• Fiddler trace (if applicable)

I hope this information helps clarify the situation and guides you toward the next steps. If you have any updates or need further assistance with the transition, feel free to reach out. 

Best Regards, 

Demi-N | Microsoft Community Support Specialist