The calendar events on my latest preset seem to be being duplicated. I have gotten confirmation from others that it happens on their devices, too, and have double and triple checked that my formulas are correct. 
Maybe you have differents calendars with the same events, and all calendars are selected in the settings of your Kustom app. Kustom apps don't discriminate the events if are duplicated. If you need all of your calendars selected in Kustom app, probably you are going to see this. you can disable one of the calendars that duplicate the other.
After some experimentation, it happens when I have "Holidays in United States" selected. Other events are not duplicated, only holidays.
Yes the problems that I see are the most with holidays, you can disable it in the settings of your Kustom app, or live with this 😁 in the events item.