Outlook Freezing, Slow Starts – Microsoft Fixes Issue
Microsoft has fixed a known issue for Outlook affecting users on Microsoft 365 since June.
The issue has been causing sow starts and freezing, almost as if Offline Outlook Data Files (OST) were syncing directly after launching Outlook.
Strangely, despite Outlook behaving as if it were syncing OST files, no new OST files are generated on affected systems and there are no new entries in the application log relating to this behaviour.
Affected users report that Outlook would open promptly if the application was closed after launch and then reopened. Microsoft noted that users might encounter difficulties starting the application on systems with airplane mode enabled.
If outlook is launched with airplane mode enabled, an error message appears, stating, “Cannot start Microsoft Outlook. Cannot open the Outlook Window. The set of folders cannot be opened. The attempt to log on to Microsoft Exchange has failed”.
These issues with Outlook freezing and experiencing slow starts would happen during cache re-priming, which is a process triggered when creating new profiles or when disabling shared calendar improvements.
Microsoft states, “One known cause of this symptom is cache re-priming. This is expected if the user has created a new profile, or manually toggled from REST to MAPI by disabling Shared Calendar Improvements”.
Microsoft continues, “However, due to endemic problems in reading service enabled feature’s status in non-Office MAPI based applications, running such apps can force this toggle unexpectedly”.
This Outlook issue has been resolved in build 16929.15000 and has been released to the beta channel. The fix is set to roll out to the current channel in late November via builds 17029.20000 and higher.
Currently, affected users can work around the issue by enabling the “Shared Calendar Improvements” option in the Exchange Account Settings dialog. This can be done by clicking More Settings and selecting the “Advanced” tab. The changes will take affect after restarting Outlook.
