Check your caldav config files in /userdata/config/org/openhab/, there may be wrong values compared to your caldav cfg files.
BEGIN:VCALENDAR
PRODID:-//Mozilla.org/NONSGML Mozilla Calendar V1.1//EN
VERSION:2.0
BEGIN:VTIMEZONE
TZID:Europe/Berlin
BEGIN:DAYLIGHT
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:19700329T020000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
DTSTART:19701025T030000
RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
CREATED:20171105T204207Z
LAST-MODIFIED:20181126T160638Z
DTSTAMP:20181126T160638Z
UID:XXXXXXXXXXXXXXXXXX
SUMMARY:Xmas_Lights_Enable_Proxy
STATUS:CONFIRMED
RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=-1MO
DTSTART;TZID=Europe/Berlin:20181126T150000
DTEND;TZID=Europe/Berlin:20190104T230000
CLASS:PUBLIC
SEQUENCE:21
DESCRIPTION:BEGIN:Xmas_Lights_Enable_Proxy:ON\nEND:Xmas_Lights_Enable_Pro
xy:OFF
X-MOZ-GENERATION:12
END:VEVENT
END:VCALENDAR
This event was set up via Lightning in Thunderbird on a nextCloud Server.