Our organization of around 400 people has a select few who have an issue with calendar events reappearing. They are both single events and recurring events. We have tried deleting them from Outlook online but that does not resolve the issue. I have talked with a Microsoft Support representative about using PowerShell to delete individual events that are possibly corrupt. At this point that would be very time consuming and I am looking for a cause and permanent fix for this problem. Any ideas are appreciated.
The only time (so far) that we have had problems with scheduling is when someone is manipulating calendar events with an iPhones built in app. Tell your users to use the OWA app for all devices (android and iOS). You will see a dramatic drop in issues.