Sonar Add-in Missing in Outlook after M365 update today

Question

We have investigated the issue with the Sonar outlook add-in not appearing in Outlook Classic, while it is still working in OWA.

After reviewing with the vendor, no issues were found with the add-in itself or its configuration on our side.

According to the vendor, this issue is likely related to a known Microsoft bug (reported on March 23) affecting admin-deployed add-ins:

https://learn.microsoft.com/en-us/office/dev/add-ins/resources/resources-office-add-in-known-issues

Current status:

• Add-in works normally in OWA
• Missing in Outlook Classic on some machines that update M365 to new version , some computer that not update yet still can use
• Reinstalling the add-in does not resolve the issue

Request:

Pls help find solution or Estimated timeline for fix (if available)

Thank you

Answer 1

Hi @Tommy

Based on the information you provided, I understand that the Sonar Outlook add-in is currently missing in Outlook Classic following a recent Microsoft 365 update, although it continues to function perfectly in OWA. I also note that reinstalling hasn't resolved the issue, and your vendor has linked this to a known Microsoft bug reported on March 23 affecting admin-deployed add-ins.

I truly appreciate you sharing these details and your proactive troubleshooting efforts. First, please note that this is a user-to-user support forum. Moderators and contributors, including Microsoft employees participating externally, do not have the permissions or resources to directly intervene in Microsoft product features or access internal backend systems. Our role here is focused on sharing technical guidance based on publicly available documentation and practical experience to assist you in your resolution efforts.

Because the development team is currently investigating issues related to Office add-ins, it is highly likely, as you mentioned, that this ongoing situation is directly impacting the functionality of admin-deployed add-ins. In this case, I kindly ask for your patience to wait a short while for the development team to complete their investigation and roll out a definitive fix.

If possible, could you please refer to the initial response as well? Additionall, I will continue to monitor the situation closely and will notify you as soon as there are any further updates or an estimated timeline for the fix.

Thank you for your understanding.

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Answer 2

The described behavior matches a current Microsoft issue with admin‑deployed Office add-ins.

From the known-issues article:

• There is an “Intermittent failure to load or deploy Office Add-ins” problem where add-ins are visible in the admin experience but do not render or appear correctly in Office/Outlook clients.
• A related, more detailed entry describes intermittent failures to load or deploy Office Add-ins due to Exchange authentication changes, where add-ins can appear missing or fail to deploy, especially for tenants impacted by recent EWS security enforcement.
• Status for that issue is Open, and Microsoft has begun rolling out mitigations. The article does not provide a specific ETA for full resolution.
• The guidance states no customer action is required; Microsoft is applying targeted mitigations. Tenants that continue to experience issues are advised to contact Microsoft Support.

Given the symptoms:

• Add-in works in Outlook on the web.
• Add-in is missing in some updated Outlook Classic clients.
• Reinstalling the add-in does not help.

This aligns with the known issue. There is no documented client-side fix or registry change for this specific problem. The recommended actions are:

1. Confirm the issue matches the known problem
   • Verify the add-in is still visible and correctly configured in the Microsoft 365 admin center (centralized deployment).
   • Confirm that affected users see the add-in in OWA but not in Outlook Classic, as described.
2. Use Outlook on the web as a temporary workaround
   • Since the add-in functions correctly in OWA, direct affected users to use OWA for workflows that depend on the Sonar add-in until the fix is fully deployed.
3. Open a support ticket with Microsoft
   • Because the status is “Open” and mitigation is in progress, and no tenant-side fix is documented, the official guidance is to contact Microsoft Support if the issue persists.
   • Support can confirm whether the tenant is on a mitigated build, provide any interim workarounds, and share the most current internal ETA.
4. Monitor the known-issues page
   • Track the “Intermittent failure to load or deploy Office Add-ins” and the “Intermittent failure to load or deploy Office Add-ins due to Exchange authentication changes” entries for status updates. Any published ETA or resolution will appear there.

There is no published estimated timeline for full resolution in the provided documentation; only that mitigation has begun rolling out and the issue remains open.

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References:

• Office Add-ins known issues
• Office add-ins are not displayed correctly in Outlook
• Outlook add-ins overview
• Sideload Outlook add-ins for testing
• Make your Office Add-in compatible with an existing COM or VSTO add-in
• Compare Outlook add-in support in Outlook on Mac with other Outlook clients
• Unable to add apps within Outlook, get "Something went wrong" generic error message - Microsoft Q&A
• Outlook ask for credentials every minute - Microsoft Q&A
• Office 365 apps insist on using Outlook Classic to share documents to email - Microsoft Q&A
• How to fix the issue with MS Office asking you to log in every time you open an Office app - Microsoft Q&A
• since the office upgrade, my title bar overlaps my ribbon bar, this is a major **** and quite annoying - Microsoft Q&A