Calendar view not displaying properly

Hi,

My calendar view messed up this last week. This month (August) looks fine, but September is blank for the first half of the month, with August events duplicated in the last two September weeks. October onwards and all months prior are empty. 

I see the problem in day, week, and month views.

The planner view shows all events correctly, as far as I can tell, so it seems to be a display issue rather than a sync issue.

Thanks, J