Known issues

What Microsoft lists as broken, worked around, or changing in a way that breaks things: Windows release health, Office, Microsoft Graph, SQL Server and Exchange Server updates, and the identity platform. Status is shown as Microsoft publishes it, and ChangeIntel notes when Microsoft revises an entry.

Windows releases

Exchange Server updates

source checked 1d ago

9 update articles checked, 5 with no known issues

KB5128895Exchange Server SE RTM Oct26SU13 Oct 2026no known issues listed
KB5129955Exchange Server SE RTM Sep26SUv22 Oct 20263 known issues
- Availability (free/busy) fails for delegated mailboxes in Exchange hybrid deployments that use Graph API only
  2 Oct 2026
  In a classic hybrid deployment that's configured by using ConfigureExchangeHybridApplication.ps1 -UseGraphApiOnly, availability (free/busy) information fails when a remote mailbox user accesses a delegated on-premises mailbox and checks…
2 resolved issues
- Resolved in KB5128895A published calendar (.ics) returns "HTTP 500" for calendar applications
  2 Oct 2026
  After you install the August 2026 security update (Exchange Server SE, build 15.2.2562.46), subscriptions to an anonymously published Exchange calendar stop refreshing. The subscribing application reports a server error, and the URL…
  Revised 16 Oct 2026: the text changed
- Resolved in KB5128895A ContentEngine deadlock occurs because of missing Korean WordBreaker rule files
  2 Oct 2026
  After you install the September 2026 Security Update for Microsoft Exchange, Exchange environments that process email messages that contain Korean language content might experience one or more of the following symptoms: Search results…
KB5121608Exchange Server SE RTM Sep26SU8 Sep 20263 known issues
- Availability (free/busy) fails for delegated mailboxes in Exchange hybrid deployments using Graph API only
  8 Sep 2026
  In a classic hybrid deployment that's configured by using ConfigureExchangeHybridApplication.ps1 -UseGraphApiOnly, availability (free/busy) information fails when a remote mailbox user accesses a delegated on-premises mailbox and checks…
2 resolved issues
- Resolved in KB5128895Published calendar (.ics) returns HTTP 500 for calendar applications
  8 Sep 2026
  After you install the August 2026 security update (Exchange Server SE, build 15.2.2562.46), subscriptions to an anonymously published Exchange calendar stop refreshing. The subscribing application reports a server error, and the URL…
  Revised 16 Oct 2026: the text changed
- Resolved in KB5128895ContentEngine deadlock because of missing Korean WordBreaker rule files
  8 Sep 2026
  After you install the September 2026 Security Update for Microsoft Exchange, Exchange environments that process email messages that contain Korean language content might experience one or more of the following symptoms: Search results…
KB5128896Exchange Server 2019 CU15 Oct26SU13 Oct 2026no known issues listed
KB5128897Exchange Server 2019 CU14 Oct26SU13 Oct 2026no known issues listed
KB5129956Exchange Server 2019 CU15 Sep26SUv22 Oct 20261 known issue
1 resolved issue
- Resolved in KB5128896A published calendar (.ics) returns "HTTP 500" for calendar applications
  2 Oct 2026
  After you install the August 2026 security update (Exchange Server SE, build 15.2.2562.46), subscriptions to an anonymously published Exchange calendar stop refreshing. The subscribing application reports a server error, and the URL…
  Revised 16 Oct 2026: the text changed
KB5128898Exchange Server 2016 CU23 Oct26SU13 Oct 2026no known issues listed
KB5129958Exchange Server 2016 CU23 Sep26SUv22 Oct 20261 known issue
1 resolved issue
- Resolved in KB5128898A published calendar (.ics) returns "HTTP 500" for calendar applications
  2 Oct 2026
  After you install the August 2026 security update (Exchange Server SE, build 15.2.2562.46), subscriptions to an anonymously published Exchange calendar stop refreshing. The subscribing application reports a server error, and the URL…
  Revised 16 Oct 2026: the text changed
KB5121611Exchange Server 2016 CU23 Sep26SU8 Sep 2026no known issues listed

From the "Known issues in this update" section of each update's support article, for the newest updates of each version on Microsoft's build page. An article without that section lists no known issues.