thank you for your message! Do the duplicates belong to the same calendar? Is it a Google calendar? Please try to re-download the affected calendar: Open "Settings > Visibility/Download" and set the holiday calendar to "Forced redownload once, visible". Then return to the calendar view and select "Sync" from the menu. Does that fix it?
Please try this and don't hesitate to contact me again if you still have problems or if you have any questions!
Kind regards
Dominique Gunia