Microsoft has officially confirmed the problem was on their end, and published communication about this incident to the Service Health section of the Microsoft 365 Admin Center for all affected tenants (Communication ID: EX829938). You can find it in the “Issue history” section. We also pasted it below:
User impact
Users may have been unable to use already acquired add-ins within the Outlook desktop app and Outlook on the web.
More info
The issue could have been seen in either the new or classic Outlook desktop app, as well as within the Outlook mobile app.
Scope of impact
This issue may have affected any user of already acquired add-ins within the new or classic Outlook desktop app, Outlook on the web, and the Outlook mobile app.
Root cause
A recent code change resulted in a bug affecting the service that gets add-in manifests into the host, which led to this impact.
Next steps
-We’re (Microsoft) reviewing our code change testing and validation procedures to assess areas for improvement to avoid similar issues from being reintroduced in the future.
- We’re (Microsoft) refining our understanding of the code bug by reviewing what the code change intended to do and analyzing how it led to this behavior, so that we can better understand how it caused the impact.