Resolved
There are no more Defender email check delays.
The issue has been mitigated and will be continued to be investigated to prevent this from occurring again.
Monitoring
Most Defender checks are no longer lagging, however we are still seeing a delay with a small portion of Defender emails being checked.
We are continuing our investigation and resolution of this issue.
Identified
We are seeing delayed Defender checks for Inbound emails. For COM add-in users , emails wont be checked until they click the email. For Gateway users, emails will not be checked. Defender via API users will have delayed checks and may be prevented from releasing/deleting emails from quarantine. We will reprocess these requests when the service is back up.
We are looking into this and will provide updates here.