looks like the caldav to ics doesn’t produce the info in the format the latest code expects. (ISOStrings)
i think this is another bug. I suggest you open an issue on github for MagicMirror so someone can look at it eventually. (This is all volunteer, and anyone can propose a fix)
comment in calendarfetcher.js is// ical.js started returning recurrences and exdates as ISOStrings without time information.