I am having a similar issue. When I change or move an event on my Google Calendar it either doesn’t change at all on my events calendar or it created another event so that there are now two. I figured to get around this whenever I made changes to my google calendar I would clear my events calendar by deleting the events and re-import them from my recurring feed. My events are now deleted and the feed is not importing any of the events so now my calendar is completely blank.