it is about the interruption of the iCloud and Outlook sync calendar. All the usual settings, marked calendars for sync, however, nothing is displayed, that is, 0 kilobytes are displayed when moving the mouse over the calendar. On the web interface of Microsoft Outlook and iCloud, tasks and events are properly displayed.
Same problem here but using emClient on Windows 10 desktop! … my emails work fine - so like another poster I am now using One Calendar on Windows 10 and my Android phone - which works perfectly.