Intercalendary function doesn't work as intended in calendars. Especially the "Offset the beginning of this event one day forward" button. If this is engaged, every time you save the calendar the date of the event is pushed forward one day. Like, if the event is supposed to be on 11/23 and you refresh or save the page, it'll count up to 24, then 25 and so on.

I've been unable to accomplish a lead year set up at all, despite excessive trouble shooting

Tried to resolve on both google chrome and Brave

just play around with it. should be pretty clear it doesn't work right. I was working on the last day of the year in my world.