The problem starts when you try to update a single event of a recurring event that has attendees. I can make a recurring event for every week on Monday at 1pm. After that I go and change next Monday to 2pm. I select this event only in dialog box. It will appear as it sent the update to the invitees however it never does. The event shows the changed time on sierra calendar however it does not update the office365 calendar neither in OWA or any other device connected including IOS devices. It also does not update the invited persons calendar. The only way I can get this to work is by changing the events in IOS or in OWA. I am able to reproduce this on several different exchange servers and OS X back to El Capitan. It works perfect in Mountain Lion. I have opened a ticket with apple and Microsoft and both point their fingers back at the other. Boss is super frustrated that we spent all this money on O365 and he can't use his calendar without a work around.