Hi @Aussupport30
Currently there is an active service incident about this symptom EX496574
This is the last update from this report:
February 9, 2023 11:03 PM
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Title: Some delegate users' unprocessed meetings may not show as tentative on their calendar in Exchange Online
User impact: Delegate users' unprocessed meetings may not show as tentative in Exchange Online.
More info: Affected users may also see general delegate calendar sync issues where updates and edits made for meetings may not be reflected on delegate calendars for up to three hours, after which an automatic sync applies the changes. This issue may occur through any connection method for affected delegate users. From the principal user's calendar view, the new meeting displays correctly as tentative. When some delegates view affected meeting requests, the calendar view from the invite displays the following error: "We couldn't find this meeting in the calendar. It may have been moved or deleted." If the delegate processes the invite (Accept/Tentative), they then see the calendar item show in their copy of the principal's calendar.
While the fix is continuing to saturate throughout the affected environments, please try turning off shared calendar improvements for affected users in the Outlook desktop client to bypass the issue. Once the fix is fully saturated, please turn shared calendar improvements back on for those users to avoid performance issues. Instructions can be found here:
https://support.microsoft.com/en-us/office/how-to-enable-and-disable-the-outlook-calendar-sharing-up...
We'd like to get your feedback on the workaround we provided. From a non-mobile device, please rate this post and submit it in the textbox.
Current status: The fix is almost fully saturated and has reached 99.9 percent of the affected infrastructure, so most users are no longer impacted. We're monitoring as the fix progresses for the remainder of infrastructure to ensure all of the user impact gets remediated.
Scope of impact: Impact may occur for some delegate users attempting to view unprocessed meetings received by the principal user or apply delegate calendar updates and edits made for meetings.
Start time: Wednesday, December 21, 2022, 6:00 PM (12/22/2022, 12:00 AM UTC)
Root cause: A recent service update that was intended to optimize service functionality introduced a code regression and is inadvertently causing impact.
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Next update by: Friday, February 17, 2023, 4:30 AM (10:30 AM UTC)
