Outlook add-in fails to load on O365 Desktop Client

Since I updated Office 365 to Version 1908 (Build 11929.20658) I am having issues using our own developed Outlook add-in in the Outlook Desktop Client. Outlook reports the following error: "ADD-IN ERROR This add-in could not be started. Close this dialog to ignore the problem or click "Restart" to try again"

The same add-in works fine in the Outlook Web in different browsers (IE, Chrome, Edge).

I followed the instructions from https://docs.microsoft.com/en-us/office/dev/add-ins/outlook/troubleshoot-outlook-add-in-activation, but it didn't help to solve the issue.

Looking into Fiddler logs, it seems that the Outlook doesn't try to reach the server to download the add-in files.

I read about Enable Protected Mode on IE https://docs.microsoft.com/en-us/office/troubleshoot/error-messages/apps-for-office-not-start However, the newer Office version uses EdgeView as a web browser engine. I also have installed on this machine the Edge Chromium version.

• Is a similar configuration change need also on EdgeView?
• Is there a way to troubleshoot the or collect logs when starting up the add-in inside Outlook desktop?

I rolled back Office 365 to Version 1902 (Build 11328.20492). In this version, the add-ins work fine.

But, when updating to the latest version available Version 2002 (Build 12527.20278) the problem remains.

I've attached screenshots from Outlook Destkop (Error) and Outlook Web (OK) as additional information.

Looking into the Event Viewer / Windows Logs / Application I see the following Application Error(s) when opening the add-in inside Outlook Desktop

Event 1000, Application Error

Faulting application name: Win32WebViewHost.exe, version: 10.0.18362.329, time stamp: 0x65f1ccce Faulting module name: edgemanager.dll, version: 11.0.18362.693, time stamp: 0xb50be940 Exception code: 0xc0000409 Fault offset: 0x0000000000032baf Faulting process id: 0x15b0 Faulting application start time: 0x01d5f97c03220670 Faulting application path: C:\Windows\SystemApps\Microsoft.Win32WebViewHost_cw5n1h2txyewy\Win32WebViewHost.exe Faulting module path: C:\WINDOWS\SYSTEM32\edgemanager.dll Report Id: 240488bf-a9e4-43ef-abc6-832c8b0f8a79 Faulting package full name: Microsoft.Win32WebViewHost_10.0.18362.449_neutral_neutral_cw5n1h2txyewy Faulting package-relative application ID: DPI.PerMonitorAware

Event 1000, Application Error

Faulting application name: RuntimeBroker.exe, version: 10.0.18362.1, time stamp: 0x4539d5a0 Faulting module name: EdgeManager.dll, version: 11.0.18362.693, time stamp: 0xb50be940 Exception code: 0xc0000409 Fault offset: 0x0000000000022f44 Faulting process id: 0x18d8 Faulting application start time: 0x01d5f97c035dfbc5 Faulting application path: C:\Windows\System32\RuntimeBroker.exe Faulting module path: C:\Windows\System32\EdgeManager.dll Report Id: 9add408f-632f-4b25-8786-eced0492536d Faulting package full name: Microsoft.Win32WebViewHost_10.0.18362.449_neutral_neutral_cw5n1h2txyewy Faulting package-relative application ID: runtimebroker07f4358a809ac99a64a67c1

I have the same issue with VDI.

To solve this issue I try :

• Reinstall M365

• Delete Microsoft folder into the user's profile :

  c:\users\username\appdata\local\microsoft  
  c:\users\username\appdata\locallow\microsoft  
  c:\users\username\appdata\roaming\microsoft*
  

It seems to be a profile issue because when I delete the user's profile, everything works perfectly. I perform some test on a user profile to find the correct file