add three lines
modules/default/calendarcalendarfetcherutils.js

					event.start = rule.options.dtstart;  // old code line 294
                                        // insert these three lines
					if((rule.options.until != undefined) && CalendarFetcherUtils.isFullDayEvent(event)){
						Log.debug("fixup rrule until")
						rule.options.until = new Date(new Date(moment(rule.options.until).startOf("day").add(1,"day")).getTime())
					}

					Log.debug("fix rrule start=", rule.options.dtstart); // old code line 301

so its a source problem. the parser processed this correctly.
we have no idea why its set like this, we just process the ICS data.

but the until is weird

Until Oct 08 (in the UI) , which isn’t a Tuesday, so the event could not happen then anyhow.
I’d try changing that and see what happens with the ICS data

[2025-10-07 07:52:10.434] [DEBUG] parsed data={
"040000008200E00074C5B7101A82E008000000004ECDB12BC10FDC01000000000000000010000000012DADF723AF8140B35A2E374506E8D9": {
    "type": "VEVENT",
    "params": [],
    "rrule": {
      "_cache": {
        "all": false,
        "before": [],
        "after": [],
        "between": []
      },
      "origOptions": {
        "tzid": "Europe/London",
        "dtstart": "2025-08-26T17:45:00.000Z",
        "freq": 2,
        "until": "2025-10-07T16:45:00.000Z",
        "interval": 1,
        "byweekday": [
          {
            "weekday": 1
          }
        ],
        "wkst": {
          "weekday": 0
        }
      },
      "options": {
        "freq": 2,
        "dtstart": "2025-08-26T17:45:00.000Z",
        "interval": 1,
        "wkst": 0,
        "count": null,
        "until": "2025-10-07T16:45:00.000Z",
        "tzid": "Europe/London",
        "bysetpos": null,
        "bymonth": null,
        "bymonthday": [],
        "bynmonthday": [],
        "byyearday": null,
        "byweekno": null,
        "byweekday": [
          1
        ],
        "bynweekday": null,
        "byhour": [
          17
        ],
        "byminute": [
          45
        ],
        "bysecond": [
          0
        ],
        "byeaster": null
      }
    },
    "exdate": [],
    "uid": "040000008200E00074C5B7101A82E008000000004ECDB12BC10FDC01000000000000000010000000012DADF723AF8140B35A2E374506E8D9",
    "summary": "My Event",
    "start": "2025-08-26T16:45:00.000Z",
    "datetype": "date-time",
    "end": "2025-08-26T17:30:00.000Z",
    "class": "PUBLIC",
    "priority": "5",
    "dtstamp": "2025-10-07T06:52:10.000Z",
    "transparency": "OPAQUE",
    "status": "CONFIRMED",
    "sequence": "0",
    "location": "",
    "MICROSOFT-CDO-APPT-SEQUENCE": "0",
    "MICROSOFT-CDO-BUSYSTATUS": "BUSY",
    "MICROSOFT-CDO-INTENDEDSTATUS": "BUSY",
    "MICROSOFT-CDO-ALLDAYEVENT": "FALSE",
    "MICROSOFT-CDO-IMPORTANCE": "1",
    "MICROSOFT-CDO-INSTTYPE": "1",
    "MICROSOFT-DONOTFORWARDMEETING": "FALSE",
    "MICROSOFT-DISALLOW-COUNTER": "FALSE",
    "MICROSOFT-REQUESTEDATTENDANCEMODE": "DEFAULT",
    "MICROSOFT-ISRESPONSEREQUESTED": "FALSE",
    "method": "PUBLISH"
  }
}]

The timezone does look to be getting updated to the IANA string. But line 33 has:

"until": "2025-10-07T16:45:00.000Z",

but the final event should be starting at 17:45 and ending at 18:30. So the ical does seem to imply that the series ends prior to the final event starting. Even if we account for the hour difference due to a potential timezone issue, the series is ending right as the final event starts.

Is there a particular part of the log that might be useful for digging deeper - a search string I can use to narrow things down? Or are we just looking at another Microsoft quirk…

stop MM

, "DEBUG"

to the logLevel value in config.js at the top
and then start MM in debug mode

cd ~/MagicMirror
npm start >somefile.txt 2>&1

wait til the calendar is up
then
ctrl-q on the MM screen to shut it down

then examine somefile.txt
(careful if posting, the debug log contains the full URL of the calendar from config.js)

I’ve been digging into the iCal stuff and I see the windowsZones.json file which I presume does your MS to IANA mapping. In there is this line:

"GMT Standard Time":{"iana":["Europe/London"]}

Is that what you were referring to - should this not replace the GMT timezone with the IANA equivalent? I’m just wading through code I only partially understand…!

I can ask a few people for sample icals to see if my GTM timezone is an oddity if that’s any use.

               Local time: Mon 2025-10-06 20:26:51 BST
           Universal time: Mon 2025-10-06 19:26:51 UTC
                 RTC time: Mon 2025-10-06 19:26:51
                Time zone: Europe/London (BST, +0100)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

Is there something I need to do to try and resolve this? My MS calendar is set to a UTC timezone:

Sept 30 was excluded

So all the iCal entry looks good except for the timezone

We do not use the custom timezone configuration in the iCal data
We use the worldwide standard IANA tz names
(Why one needs custom timezones is beyond me)

Because so many users use MS products , I wrote a lookup table 5 years ago for the calendar parser we use, node-iCal

But

GMT Standard Time

Is not in that table (GMT has long been replaced by UTC)

UTC Standard Time

Is in the table

If the tz lookup fails, we use the local system timezone

I’m apparently still having an issue where events in my Outlook calendar can under certain circumstances not appear on my MM. This is again a symptom of the event’s rrule ending prior to the last event in the series. Some ICS code below:

BEGIN:VCALENDAR
METHOD:PUBLISH
PRODID:Microsoft Exchange Server 2010
VERSION:2.0
X-WR-CALNAME:My Calendar
BEGIN:VTIMEZONE
TZID:GMT Standard Time
BEGIN:STANDARD
DTSTART:16010101T020000
TZOFFSETFROM:+0100
TZOFFSETTO:+0000
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=10
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:16010101T010000
TZOFFSETFROM:+0000
TZOFFSETTO:+0100
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=3
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
RRULE:FREQ=WEEKLY;UNTIL=20251007T164500Z;INTERVAL=1;BYDAY=TU;WKST=MO
EXDATE;TZID=GMT Standard Time:20250930T174500
UID:040000008200E00074C5B7101A82E008000000004ECDB12BC10FDC01000000000000000
 010000000012DADF723AF8140B35A2E374506E8D9
SUMMARY:My Event
DTSTART;TZID=GMT Standard Time:20250826T174500
DTEND;TZID=GMT Standard Time:20250826T183000
CLASS:PUBLIC
PRIORITY:5
DTSTAMP:20251006T181942Z
TRANSP:OPAQUE
STATUS:CONFIRMED
SEQUENCE:0
LOCATION:
X-MICROSOFT-CDO-APPT-SEQUENCE:0
X-MICROSOFT-CDO-BUSYSTATUS:BUSY
X-MICROSOFT-CDO-INTENDEDSTATUS:BUSY
X-MICROSOFT-CDO-ALLDAYEVENT:FALSE
X-MICROSOFT-CDO-IMPORTANCE:1
X-MICROSOFT-CDO-INSTTYPE:1
X-MICROSOFT-DONOTFORWARDMEETING:FALSE
X-MICROSOFT-DISALLOW-COUNTER:FALSE
X-MICROSOFT-REQUESTEDATTENDANCEMODE:DEFAULT
X-MICROSOFT-ISRESPONSEREQUESTED:FALSE
END:VEVENT
END:VCALENDAR

I’m not sure if this is something that can be resolved, or why it happens but I suspect some timezone issue as I’m based in the UK and we have to endure changing the clocks twice a year.

Having said that, the ICS file does not reflect the settings in the calendar for that event:

Anyone got any suggestions? Sorry to be a pest with this one!

please check there

I’m afraid this issue has reoccurred on an event that is not full day but instead is supposed to be the last in a series. I believe it’s the same issue though where the timezone / BST is causing the problem.

Sample ICS data below:

BEGIN:VCALENDAR
METHOD:PUBLISH
PRODID:Microsoft Exchange Server 2010
VERSION:2.0
X-WR-CALNAME:Test Calendar
BEGIN:VTIMEZONE
TZID:GMT Standard Time
BEGIN:STANDARD
DTSTART:16010101T020000
TZOFFSETFROM:+0100
TZOFFSETTO:+0000
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=10
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:16010101T010000
TZOFFSETFROM:+0000
TZOFFSETTO:+0100
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=3
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
RRULE:FREQ=WEEKLY;UNTIL=20250630T173000Z;INTERVAL=1;BYDAY=MO;WKST=MO
UID:040000008200E00074C5B7101A82E00800000000E05582F27408DB01000000000000000
 010000000E892CDFA6C0E4E4298E1C987B4791120
SUMMARY:Calendar Event
DTSTART;TZID=GMT Standard Time:20250331T183000
DTEND;TZID=GMT Standard Time:20250331T200000
CLASS:PUBLIC
PRIORITY:5
DTSTAMP:20250630T164141Z
TRANSP:OPAQUE
STATUS:CONFIRMED
SEQUENCE:0
LOCATION:
X-MICROSOFT-CDO-APPT-SEQUENCE:0
X-MICROSOFT-CDO-BUSYSTATUS:BUSY
X-MICROSOFT-CDO-INTENDEDSTATUS:BUSY
X-MICROSOFT-CDO-ALLDAYEVENT:FALSE
X-MICROSOFT-CDO-IMPORTANCE:1
X-MICROSOFT-CDO-INSTTYPE:1
X-MICROSOFT-DONOTFORWARDMEETING:FALSE
X-MICROSOFT-DISALLOW-COUNTER:FALSE
X-MICROSOFT-REQUESTEDATTENDANCEMODE:DEFAULT
X-MICROSOFT-ISRESPONSEREQUESTED:FALSE
END:VEVENT
END:VCALENDAR

I’ve stripped out most of the content other than the event in question and the timezone info.

You’ll see that the DTSTART and DTEND data shows the correct start and end time but the RRULE shows the UNTIL as an hour before the event so the event does not show on the MM calendar module.

The event in Outlook shows the series being every Monday until 1st July.

I’m not sure if this “bug” is a problem with Outlook or MagicMirror.

Happy to start a new thread, or log a bug on GitHub if either of those is preferrable.

note upgrade is a two part process
test, do nothing (highlight exposed files, if any)
do upgrade

add three lines
modules/default/calendarcalendarfetcherutils.js

					event.start = rule.options.dtstart;  // old code line 294
                                        // insert these three lines
					if((rule.options.until != undefined) && CalendarFetcherUtils.isFullDayEvent(event)){
						Log.debug("fixup rrule until")
						rule.options.until = new Date(new Date(moment(rule.options.until).startOf("day").add(1,"day")).getTime())
					}

					Log.debug("fix rrule start=", rule.options.dtstart); // old code line 301

BEGIN:VEVENT
DESCRIPTION:\n
RRULE:FREQ=YEARLY;UNTIL=20250504T230000Z;INTERVAL=1;BYMONTHDAY=5;BYMONTH=5
UID:040000008200E00074C5B7101A82E00800000000DAEF6ED30D9FDA01000000000000000
 010000000D37F812F0777844A93E97B96AD2D278B
SUMMARY:Person A's Birthday
DTSTART;VALUE=DATE:20250505
DTEND;VALUE=DATE:20250506
CLASS:PUBLIC
PRIORITY:5
DTSTAMP:20250428T133000Z
TRANSP:TRANSPARENT
STATUS:CONFIRMED
SEQUENCE:0
LOCATION:
X-MICROSOFT-CDO-APPT-SEQUENCE:0
X-MICROSOFT-CDO-BUSYSTATUS:FREE
X-MICROSOFT-CDO-INTENDEDSTATUS:BUSY
X-MICROSOFT-CDO-ALLDAYEVENT:TRUE
X-MICROSOFT-CDO-IMPORTANCE:1
X-MICROSOFT-CDO-INSTTYPE:1
X-MICROSOFT-DONOTFORWARDMEETING:FALSE
X-MICROSOFT-DISALLOW-COUNTER:FALSE
X-MICROSOFT-REQUESTEDATTENDANCEMODE:DEFAULT
X-MICROSOFT-ISRESPONSEREQUESTED:FALSE
END:VEVENT

And here is a working event:

BEGIN:VEVENT
DESCRIPTION:\n
RRULE:FREQ=YEARLY;UNTIL=20250503T000000Z;INTERVAL=1;BYMONTHDAY=3;BYMONTH=5
UID:040000008200E00074C5B7101A82E00800000000591C9B3BAA0EDA01000000000000000
 01000000005E6F2F9D20F7947B69F54FBF0794A6D
SUMMARY:Person B's Birthday
DTSTART;VALUE=DATE:20250503
DTEND;VALUE=DATE:20250504
CLASS:PUBLIC
PRIORITY:5
DTSTAMP:20250428T133000Z
TRANSP:TRANSPARENT
STATUS:CONFIRMED
SEQUENCE:0
LOCATION:
X-MICROSOFT-CDO-APPT-SEQUENCE:0
X-MICROSOFT-CDO-BUSYSTATUS:FREE
X-MICROSOFT-CDO-INTENDEDSTATUS:BUSY
X-MICROSOFT-CDO-ALLDAYEVENT:TRUE
X-MICROSOFT-CDO-IMPORTANCE:1
X-MICROSOFT-CDO-INSTTYPE:1
X-MICROSOFT-DONOTFORWARDMEETING:FALSE
X-MICROSOFT-DISALLOW-COUNTER:FALSE
X-MICROSOFT-REQUESTEDATTENDANCEMODE:DEFAULT
X-MICROSOFT-ISRESPONSEREQUESTED:FALSE
END:VEVENT

Thanks for taking a look.