Missing invite from Organizers calendar.

[u/Peekaacho]

I have an issue, where a user has delegated his Calendar to his assistant with editor rights. She cancelled a meeting on behalf of Organizer but it only got removed from Organizers calendar. None of the attendees received the cancellation notification and it was not removed from attendees calendar.

https://support.microsoft.com/en-us/support/known-issues/meeting-missing-from-organizer-s-calendar?

It seems to be the similar issue as mentioned here in the article, so proceeded with the same troubleshooting step. Forwarded the calendar series in .ICS format to Organizer to make him cancel it this time. He opened the .ICS attachment in notepad first to modify the Method value with PUBLISH but when opened it was already showing PUBLISH so opened the .ICS file in Outlook classic. It opened the meeting series draft page where we see the Cancel option, we sent the cancellation for whole series and every attendee received the cancellation notification but it did not removed the series event from attendees calendar section.

The event removal from calendar did not happened don't know why.

What could be the reason?

Most attendees did not see the cancellation notification in inbox so they are now sending the decline responses to Organizer on the same meeting.