Editing and resyncing recurring events on Google Calendar
If you edit a recurring event on Google Calendar and apply the changes to This and all the following events, it will consider the new occurrences as new and will remove the old ones. This is the standard behavior on Google Calendar, as the updated recurring events are considered new.
When these updated "new" events are also synced to Notion, it may appear that you have duplicated events since the old ones are not deleted by default.
However, if you activated event deletion on your Notion Automation sync settings, the old occurrences will be automatically deleted and disappear from Notion.