I haven't personally experienced this problem, but I understand a few users who already have it. Very likely, users are experiencing a problem. Your device can benefit from a restart. Users are undoubtedly familiar that depending on the phone's model, restarting your smartphone requires a different procedure. Apart from that, it's possible that the iCloud calendar on the iPhone didn't sync. This really is typical of Outlook. Users simply need to disable iCloud sharing for each of the calendars before trying again.