Outlook shows iCal date changed despite it being the same date - outlook

Question

I'm generating iCal files and sending them via e-mail to the person that registered to a certain event on the intranet. This happens in an internal company network where everyone has to use MS Outlook, so I am mostly concerned that it looks correct on Outlook.
When the event on the intranet is changed, a new event invite with a current iCal is being sent to the registrant.
However, no matter what I change, the date keeps being highlighted as changed, despite the date being exactly the same as on the first iCal file.
Does anyone know why this happens?
I did try:
Increment the SEQUENCE number each time (first 0, then 1 and so on)
Set a custom (always the same) DTSTAMP
The event UID is exactly the same, proven by the fact that the existing event gets updated in Outlook
Note on the following screenshot that the location well has changed (and is also highlighted), but the date did not, but is still highlighted.
My iCal looks like this:
----__--MAILNEXTPART--__--
Content-Type: multipart/alternative; boundary="--__--MAILINNERBOUNDARY--__--"
----__--MAILINNERBOUNDARY--__--
Content-Type: text/calendar; charset="UTF-8"; method=REQUEST
Content-Transfer-Encoding: quoted-printable
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Microsoft Corporation//Outlook 14.0 MIMEDIR//EN
METHOD:REQUEST
BEGIN:VEVENT
UID:icalevent-8315-108-2019-05-03T11:00:00-2019-05-03T13:00:00
DTSTART:20190503T110000Z
SEQUENCE:2
TRANSP:OPAQUE
STATUS:CONFIRMED
DTEND:20190503T130000Z
LOCATION:Another Company\, \nAnother Street\, \nCH-1000 Lausanne
SUMMARY:Testevent for Outlook calendar
ATTENDEE:event-registrant#domain.com
CLASS:PUBLIC
DESCRIPTION:This is the description.
ORGANIZER:organizer#domain.com
DTSTAMP:20190503T110000Z
END:VEVENT
END:VCALENDAR
----__--MAILINNERBOUNDARY--__----
----__--MAILNEXTPART--__----
Note that I did try in this one to set the DTSTAMP to the event start date/time but this had no effect on the behavior, even if it lies in the future.