When a cancelled event is back on, instead of creating a new event in your Vivaldi Calendar you can simply restore the one you deleted.

To restore an event:

1. Open the main Calendar view.
2. Click on  “Trashed Events” in the top right corner of the calendar.
3. Click on the event you want to restore.

To restore the most recently deleted event, right-click on any of the timeslots in the Calendar and select “Restore Event From Trash”.