diff --git a/apps/dav/lib/CalDAV/TipBroker.php b/apps/dav/lib/CalDAV/TipBroker.php
index 03ea73549e1e0..37bd87c8540d1 100644
--- a/apps/dav/lib/CalDAV/TipBroker.php
+++ b/apps/dav/lib/CalDAV/TipBroker.php
@@ -19,6 +19,7 @@
 use Sabre\VObject\Property\Boolean;
 use Sabre\VObject\Property\ICalendar\CalAddress;
 use Sabre\VObject\Property\ICalendar\DateTime;
+use Sabre\VObject\Property\ICalendar\Duration;
 use Sabre\VObject\Recur\EventIterator;
 
 class TipBroker extends Broker {
@@ -398,16 +399,7 @@ protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo,
 				}
 			}
 
-			// determine if this attendee needs to be notified of the change, based on whether
-			// a significant property changed on the event, or the set of instances they are part of changed
-			$oldAttendeeInstances = isset($oldEventInfo['attendees'][$attendee]) ? array_keys($oldEventInfo['attendees'][$attendee]['instances']) : [];
-			$newAttendeeInstances = array_keys($eventInfo['attendees'][$attendee]['instances']);
-
-			$significantChange
-				= $eventInfo['attendees'][$attendee]['forceSend'] === 'REQUEST'
-				|| count($oldAttendeeInstances) !== count($newAttendeeInstances)
-				|| count(array_diff($oldAttendeeInstances, $newAttendeeInstances)) > 0
-				|| $oldEventInfo['significantChangeHash'] !== $eventInfo['significantChangeHash'];
+			$significantChange = $this->isSignificantChangeForAttendee($attendee, $eventInfo, $oldEventInfo);
 
 			$messages[] = $this->generateMessage(
 				$instances, $organizerHref, $organizerName, $eventInfo['attendees'][$attendee], $objectId, $objectType, $objectSequence, 'REQUEST', $template, $significantChange
@@ -417,6 +409,101 @@ protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo,
 		return $messages;
 	}
 
+	/**
+	 * Determines whether an attendee needs to be notified of a change, considering only the
+	 * occurrences the attendee takes part in before or after the change.
+	 *
+	 * A new recurrence exception that matches the occurrence it replaces, such as one created to
+	 * store another attendee's participation status, is not significant.
+	 */
+	protected function isSignificantChangeForAttendee(string $attendee, array $eventInfo, array $oldEventInfo): bool {
+		$newAttendance = $eventInfo['attendees'][$attendee]['instances'] ?? [];
+		$oldAttendance = $oldEventInfo['attendees'][$attendee]['instances'] ?? [];
+		if (($eventInfo['attendees'][$attendee]['forceSend'] ?? null) === 'REQUEST' || $oldAttendance === []) {
+			return true;
+		}
+
+		$newInstances = $eventInfo['instances'] ?? [];
+		$oldInstances = $oldEventInfo['instances'] ?? [];
+		foreach (array_keys($newInstances + $oldInstances) as $instanceId) {
+			$oldInstance = $oldInstances[$instanceId] ?? null;
+			$newInstance = $newInstances[$instanceId] ?? null;
+			// an occurrence without its own component is attended through the master
+			$wasAttending = isset($oldAttendance[$instanceId]) || ($oldInstance === null && isset($oldAttendance['master']));
+			$isAttending = isset($newAttendance[$instanceId]) || ($newInstance === null && isset($newAttendance['master']));
+			if ($wasAttending !== $isAttending) {
+				return true;
+			}
+			if ($isAttending && !$this->isSameOccurrence($oldInstance ?? $oldInstances['master'] ?? null, $newInstance ?? $newInstances['master'] ?? null)) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+	/**
+	 * Compares two components describing the same occurrence on their significant properties.
+	 *
+	 * When one of them is the master standing in for an occurrence without its own component,
+	 * the recurrence rules are ignored and the timing is compared as start and duration.
+	 */
+	protected function isSameOccurrence(?VEvent $old, ?VEvent $new): bool {
+		if ($old === null || $new === null) {
+			return false;
+		}
+
+		$oldIsException = isset($old->{'RECURRENCE-ID'});
+		if ($oldIsException === isset($new->{'RECURRENCE-ID'})) {
+			return $this->significantValues($old, $this->significantChangeProperties) === $this->significantValues($new, $this->significantChangeProperties);
+		}
+
+		[$exception, $master] = $oldIsException ? [$old, $new] : [$new, $old];
+		$properties = array_diff($this->significantChangeProperties, ['DTSTART', 'DTEND', 'DURATION', 'DUE', 'RRULE', 'RDATE', 'EXDATE']);
+		return $this->significantValues($exception, $properties) === $this->significantValues($master, $properties)
+			&& $this->getDateTimeValue($exception, 'DTSTART')?->getTimestamp() === $this->getRecurrenceKey($exception)
+			&& $this->getDurationInSeconds($exception) === $this->getDurationInSeconds($master);
+	}
+
+	/**
+	 * @param list<string> $propertyNames
+	 * @return array<string, list<string>>
+	 */
+	protected function significantValues(VEvent $component, array $propertyNames): array {
+		$values = [];
+		foreach ($propertyNames as $propertyName) {
+			foreach ($component->select($propertyName) as $property) {
+				$values[$propertyName][] = $property->getValue();
+			}
+		}
+		return $values;
+	}
+
+	protected function getDateTimeValue(VEvent $component, string $propertyName): ?\DateTimeImmutable {
+		foreach ($component->select($propertyName) as $property) {
+			if ($property instanceof DateTime) {
+				return $property->getDateTime();
+			}
+		}
+		return null;
+	}
+
+	protected function getDurationInSeconds(VEvent $component): ?int {
+		$start = $this->getDateTimeValue($component, 'DTSTART');
+		$end = $this->getDateTimeValue($component, 'DTEND');
+		if ($start !== null && $end === null) {
+			foreach ($component->select('DURATION') as $duration) {
+				if ($duration instanceof Duration) {
+					$end = $start->add($duration->getDateInterval());
+				}
+			}
+		}
+		if ($start === null || $end === null) {
+			return null;
+		}
+		return $end->getTimestamp() - $start->getTimestamp();
+	}
+
 	/**
 	 * Generates an iTip message for a specific attendee
 	 *
diff --git a/apps/dav/tests/unit/CalDAV/TipBrokerTest.php b/apps/dav/tests/unit/CalDAV/TipBrokerTest.php
index f128d7e262db5..775de3ec6c1fe 100644
--- a/apps/dav/tests/unit/CalDAV/TipBrokerTest.php
+++ b/apps/dav/tests/unit/CalDAV/TipBrokerTest.php
@@ -11,6 +11,7 @@
 use OCA\DAV\CalDAV\TipBroker;
 use Sabre\VObject;
 use Sabre\VObject\Component\VCalendar;
+use Sabre\VObject\Component\VEvent;
 use Sabre\VObject\ITip\Message;
 use Test\TestCase;
 
@@ -611,6 +612,162 @@ public function testParseEventForOrganizerScheduleForceSend(): void {
 		$this->assertFalse(isset($messages[0]->message->VEVENT->ATTENDEE['SCHEDULE-FORCE-SEND']));
 	}
 
+	/**
+	 * Tests an instance created to store one attendee's participation status, as done when processing a REPLY
+	 */
+	public function testParseEventForOrganizerCreatedInstanceWithPartstatIsNotSignificant(): void {
+		$originalCalendar = $this->createRecurringCalendarWithTwoAttendees();
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedCalendar = clone $originalCalendar;
+		$mutatedInstance = $this->createInstance($mutatedCalendar, '20240715T080000');
+		$mutatedInstance->ATTENDEE[1]['PARTSTAT'] = 'DECLINED';
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(2, $messages);
+		$this->assertEquals('mailto:attendee1@example.org', $messages[0]->recipient);
+		$this->assertFalse($messages[0]->significantChange);
+		$this->assertEquals('mailto:attendee2@example.org', $messages[1]->recipient);
+		$this->assertFalse($messages[1]->significantChange);
+	}
+
+	/**
+	 * Tests an instance created for the first occurrence, where RECURRENCE-ID equals the master DTSTART
+	 */
+	public function testParseEventForOrganizerCreatedFirstInstanceWithPartstatIsNotSignificant(): void {
+		$originalCalendar = $this->createRecurringCalendarWithTwoAttendees();
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedCalendar = clone $originalCalendar;
+		$mutatedInstance = $this->createInstance($mutatedCalendar, '20240701T080000');
+		$mutatedInstance->ATTENDEE[1]['PARTSTAT'] = 'DECLINED';
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(2, $messages);
+		$this->assertFalse($messages[0]->significantChange);
+		$this->assertFalse($messages[1]->significantChange);
+	}
+
+	/**
+	 * Tests an instance created to add an attendee to a single occurrence
+	 */
+	public function testParseEventForOrganizerCreatedInstanceAddAttendeeIsSignificantOnlyForAddedAttendee(): void {
+		$originalCalendar = $this->createRecurringCalendarWithTwoAttendees();
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedCalendar = clone $originalCalendar;
+		$mutatedInstance = $this->createInstance($mutatedCalendar, '20240715T080000');
+		$mutatedInstance->add('ATTENDEE', 'mailto:attendee3@example.org', ['CN' => 'Attendee Three', 'PARTSTAT' => 'NEEDS-ACTION']);
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(3, $messages);
+		$this->assertEquals('mailto:attendee1@example.org', $messages[0]->recipient);
+		$this->assertFalse($messages[0]->significantChange);
+		$this->assertEquals('mailto:attendee2@example.org', $messages[1]->recipient);
+		$this->assertFalse($messages[1]->significantChange);
+		$this->assertEquals('mailto:attendee3@example.org', $messages[2]->recipient);
+		$this->assertTrue($messages[2]->significantChange);
+	}
+
+	/**
+	 * Tests an instance created to remove an attendee from a single occurrence
+	 */
+	public function testParseEventForOrganizerCreatedInstanceRemoveAttendeeIsSignificantOnlyForRemovedAttendee(): void {
+		$originalCalendar = $this->createRecurringCalendarWithTwoAttendees();
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedCalendar = clone $originalCalendar;
+		$mutatedInstance = $this->createInstance($mutatedCalendar, '20240715T080000');
+		$mutatedInstance->remove($mutatedInstance->ATTENDEE[1]);
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(2, $messages);
+		$this->assertEquals('mailto:attendee1@example.org', $messages[0]->recipient);
+		$this->assertFalse($messages[0]->significantChange);
+		$this->assertEquals('mailto:attendee2@example.org', $messages[1]->recipient);
+		$this->assertTrue($messages[1]->significantChange);
+	}
+
+	/**
+	 * Tests an instance created for another occurrence than the one an attendee takes part in
+	 */
+	public function testParseEventForOrganizerCreatedInstanceIsNotSignificantForAttendeeOfOtherInstance(): void {
+		$originalCalendar = $this->createRecurringCalendarWithTwoAttendees();
+		$originalInstance = $this->createInstance($originalCalendar, '20240722T080000');
+		$originalInstance->add('ATTENDEE', 'mailto:attendee3@example.org', ['CN' => 'Attendee Three', 'PARTSTAT' => 'NEEDS-ACTION']);
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedCalendar = clone $originalCalendar;
+		$mutatedInstance = $this->createInstance($mutatedCalendar, '20240715T080000');
+		$mutatedInstance->ATTENDEE[1]['PARTSTAT'] = 'DECLINED';
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(3, $messages);
+		$this->assertEquals('mailto:attendee3@example.org', $messages[2]->recipient);
+		$this->assertFalse($messages[2]->significantChange);
+	}
+
+	/**
+	 * Tests an instance created to move a single occurrence
+	 */
+	public function testParseEventForOrganizerCreatedInstanceMovedIsSignificant(): void {
+		$originalCalendar = $this->createRecurringCalendarWithTwoAttendees();
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedCalendar = clone $originalCalendar;
+		$mutatedInstance = $this->createInstance($mutatedCalendar, '20240715T080000');
+		$mutatedInstance->DTSTART->setValue('20240715T100000');
+		$mutatedInstance->DTEND->setValue('20240715T110000');
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(2, $messages);
+		$this->assertTrue($messages[0]->significantChange);
+		$this->assertTrue($messages[1]->significantChange);
+	}
+
+	/**
+	 * Tests adding an attendee to all occurrences of a recurring event
+	 */
+	public function testParseEventForOrganizerAddAttendeeToSeriesIsSignificantOnlyForAddedAttendee(): void {
+		$originalCalendar = clone $this->vCalendar2a;
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedCalendar = $this->createRecurringCalendarWithTwoAttendees();
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(2, $messages);
+		$this->assertEquals('mailto:attendee1@example.org', $messages[0]->recipient);
+		$this->assertFalse($messages[0]->significantChange);
+		$this->assertEquals('mailto:attendee2@example.org', $messages[1]->recipient);
+		$this->assertTrue($messages[1]->significantChange);
+	}
+
+	private function createRecurringCalendarWithTwoAttendees(): VCalendar {
+		$calendar = clone $this->vCalendar2a;
+		$calendar->VEVENT->add('ATTENDEE', 'mailto:attendee2@example.org', [
+			'CN' => 'Attendee Two',
+			'CUTYPE' => 'INDIVIDUAL',
+			'PARTSTAT' => 'NEEDS-ACTION',
+			'ROLE' => 'REQ-PARTICIPANT',
+			'RSVP' => 'TRUE'
+		]);
+		return $calendar;
+	}
+
+	/**
+	 * Adds an unmodified instance of the master event for the given occurrence
+	 */
+	private function createInstance(VCalendar $calendar, string $recurrenceId): VEvent {
+		$instance = clone $calendar->VEVENT;
+		$instance->remove('RRULE');
+		$instance->add('RECURRENCE-ID', $recurrenceId, ['TZID' => 'America/Toronto']);
+		$instance->SEQUENCE->setValue(0);
+		$instance->DTSTART->setValue($recurrenceId);
+		$instance->DTEND->setValue(date('Ymd\THis', strtotime($recurrenceId) + 3600));
+		$calendar->add($instance);
+		return $instance;
+	}
+
 	public function testProcessMessageReplyDisallowsInvitationForwarding(): void {
 		$existingCalendar = clone $this->vCalendar1a;
 		$existingCalendar->VEVENT->add(TipBroker::INVITATION_FORWARDING_PROPERTY, 'FALSE');