Saving Edits of Outlook 365 Calendar Events

Opening and editing an event already save on my calendar in https://outlook.office.com/calendar/view/week, the following message is received: "Couldn't Save Event"/"Try Again".  If I hit "Try Again", the change - which originally showed after I made the edit and hit the "save" button - disappears and the message "Couldn't Save Event" appears without the previous option of "Try Again".

Having a somewhat similar issue with the PC version of Outlook where the calendar won't update after I edit an existing Outlook Calendar Event.  Thought the edit appears on the PC version, the calendar won't update (shift-F9 elicits the dreaded "Task 'email@address' reported error (0x8004060C): 'The message store has reached its maximum size..." message) until I right click the calendar folder, Properties/Clear Offline Items/Yes/Okay/Okay and the shift-F9.  Then I get the calendar back but the edited event has reverted to its previous state.  Any idea how to re-enable editing of existing calendar events?